DAS Codes Explained: A Practical Guide to U.S., PCT, and Chinese Patent Practice

Executive Summary: This article provides a practical guide to using the World Intellectual Property Organization’s Digital Access Service (“WIPO DAS”) to exchange patent priority documents in U.S., PCT, and Chinese practice. Although DAS can eliminate repeated submission of paper certified copies, an access code does not create or correct a priority claim, extend a filing deadline, or establish that retrieval succeeded. The article explains the distinct requirements for making an earlier application available, supplying accurate bibliographic information and access credentials, requesting retrieval, and confirming receipt. It addresses the USPTO’s four-digit confirmation-number and authorization procedures; the three routes available under PCT Rule 17.1, including the prepublication requirements and safeguards under Rules 17.1(c) and (d); and CNIPA’s separate deposit and retrieval procedures, Article 30 priority-document deadlines, and Article 19 confidentiality examination. The central practice recommendation is to manage DAS as a closed-loop process: deposit the correct document, obtain and transmit the code, request retrieval through the proper office, and verify that the priority document appears in the official record.

The Small Code Behind an Important Priority Right

 

Priority-document formalities are easy to underestimate. The substantive question is whether a later application is entitled to an earlier filing date, but the administrative record must also contain a proper priority claim and, when required, a certified copy of the earlier application. A missed claim, an unavailable document, or an unsuccessful electronic retrieval can place the asserted priority date at risk.

The World Intellectual Property Organization's Digital Access Service for Priority Documents, commonly called WIPO DAS, reduces that risk by allowing participating intellectual property offices to exchange priority documents electronically. Instead of ordering a paper certified copy from the first office and sending it to every later office, the applicant authorizes the later office to retrieve the as-filed application from a secure digital library. World Intell. Prop. Org., Digital Access Service (last visited Sept. 5, 2026).

The mechanism is simple, but the details vary by jurisdiction. U.S. practice turns on access authorization and the USPTO confirmation number. PCT practice turns on the route selected under Rule 17.1 and the timing of the request. Chinese practice adds CNIPA-specific deposit and retrieval procedures, shorter design-patent deadlines, and a separate foreign-filing confidentiality review for inventions or utility models accomplished in China.

What WIPO DAS Actually Does

 

DAS connects two roles. The Office of First Filing, also called the depositing office, holds the earlier application and makes a certified electronic copy available. The Office of Second Filing, also called the accessing office, handles the later application and retrieves the copy. For a PCT application, the International Bureau may act as the accessing office.

The process normally has two affirmative steps. First, the applicant ensures that the earlier application is available in DAS and obtains its access code. Second, the applicant supplies that code and the correct bibliographic data to the later office and asks that office to retrieve the document. The system does not assume consent merely because a priority claim appears in a filing. World Intell. Prop. Org., DAS User Guide (June 2, 2026).

Participation is office-specific and document-specific. An office may deposit some kinds of applications but not others, or may retrieve a different set of document types. Counsel should therefore check the current WIPO participating-office profile for both offices and for the particular application type rather than relying on a prior filing or an old docketing note.

The DAS Code: What It Is and What It Is Not

 

The DAS access code is a code associated with one deposited priority document. The later office generally uses it together with four items: the originating office code, the priority application number, the priority filing date, and the applicant's request for retrieval. The format varies by depositing office. Some codes are alphanumeric; for an eligible U.S. application, the code ordinarily is the application's four-digit USPTO confirmation number.

The code should be treated as part of the priority record, not as a general account credential. It does not permit the recipient to alter the earlier application, and it is not a substitute for a power of attorney. Its function is narrower: it allows a participating office to obtain the certified as-filed document through DAS.

Most importantly, a correct access code cannot rescue an omitted or legally defective priority claim by itself. The later filing must still identify the earlier application accurately, satisfy the applicable priority period, and comply with the receiving office's procedures. DAS addresses delivery of the evidentiary copy; it does not determine substantive entitlement to the claimed date.

Using a U.S. Application as the Priority Filing

 

The Four-Digit Confirmation Number

 

For an eligible electronically filed U.S. provisional or nonprovisional application, the DAS access code is ordinarily the four-digit confirmation number shown on the electronic acknowledgment receipt and filing receipt. Foreign or PCT counsel should receive the U.S. application number, the U.S. filing date, the office code US, and that four-digit confirmation number. U.S. Pat. & Trademark Off., Electronic Priority Document Exchange (PDX) Program (last visited Sept. 5, 2026).

Office: USApplication: 63/123,456Filing date: January 10, 2026DAS code: 9876

This outbound priority-document discussion should not be confused with a U.S. nonprovisional application's ordinary claim to the benefit of an earlier U.S. provisional or qualifying earlier U.S. nonprovisional application. Domestic-benefit claims are governed by 35 U.S.C. §§ 119(e) or 120 and 37 C.F.R. § 1.78, rather than the certified-copy and DAS workflow applicable to foreign-priority claims. The same U.S. application may, of course, still require DAS handling when it serves as the priority filing for a PCT or foreign application. 35 U.S.C. §§ 119(e), 120; 37 C.F.R. § 1.78 (2026); MPEP § 211 (9th ed. Rev. 01.2024, Nov. 2024).

Authorization Is a Separate Requirement

 

The confirmation number is usable only if the USPTO is authorized to provide access to the unpublished application. Under 37 C.F.R. § 1.14(h)(1), access may be provided to a participating office when the application contains the required written authority. A properly signed original application data sheet may provide that authority, but it must be submitted with the U.S. priority application for that mechanism to be effective. 37 C.F.R. § 1.14(h)(1) (2026).

If the authorization was omitted at filing, a later ADS cannot supply it. The applicant should use Form PTO/SB/39, or an applicant-generated equivalent, to provide the authorization after filing. The U.S. filing receipt should then be reviewed to confirm that authorization was recorded. Its outbound indicator—typically 'Permission to Access . . . Yes'—is different from the inbound retrieval indicators discussed below. A common failure occurs when foreign counsel receives the correct four-digit number but the USPTO has never been authorized to release the underlying application.

DAS authorization also does not replace a required U.S. foreign-filing license. If the invention was made in the United States, the applicant must separately comply with the statutory and regulatory foreign-filing-license rules before filing abroad. 35 U.S.C. § 184; 37 C.F.R. § 5.11 (2026).

Claiming Foreign Priority in a U.S. Application

 

Enter the Code in the ADS

 

When a U.S. application claims priority to an application filed with a participating foreign office, the applicant should obtain the foreign DAS code before filing whenever possible. The code belongs in the Foreign Priority Information section of the ADS together with the office code, application number, and filing date. If those data are properly supplied and the document is eligible, the USPTO ordinarily attempts retrieval through DAS when the application is released from the Office of Patent Application Processing.

The filing receipt provides an early diagnostic. For the relevant foreign priority claim, it should state 'Access Code Provided' and include the 'Request to Retrieve' paragraph explaining that the USPTO will attempt retrieval. Those indicators show that retrieval will be attempted; neither proves that it succeeded.

The corrective step depends on the source of the problem. If the ADS contains incorrect priority information or omits the access code, counsel should submit an appropriately marked corrected ADS and request a corrected filing receipt. Correcting the priority claim itself after the applicable deadline may also require a petition under 37 C.F.R. § 1.55(e), although supplying a late access code alone is not necessarily a late priority claim. If the ADS was accurate but the filing receipt does not reflect the submitted information, counsel should request correction of the filing receipt. If both records are correct but the document remains absent after the ordinary retrieval interval, counsel should verify DAS availability and escalate the retrieval failure rather than file another ADS merely because retrieval has not occurred. 37 C.F.R. §§ 1.55(d)(1), (e), (i)(2), 1.76(b)(6), (c) (2026); U.S. Pat. & Trademark Off., Electronic Priority Document Exchange (PDX) Program (updated July 9, 2026).

A proper ADS priority claim and DAS code normally trigger direct retrieval automatically. Form PTO/SB/38 is generally reserved for the indirect procedure under 37 C.F.R. § 1.55(i)(4), in which the certified copy of an application from a nonparticipating office is held in an eligible European Patent Office or Japan Patent Office file; it is not ordinarily required for a direct DAS retrieval. 37 C.F.R. § 1.55(i)(4) (2026).

The Claim and the Certified Copy Remain Distinct

 

For a U.S. application filed under 35 U.S.C. § 111(a), other than a design application, the foreign priority claim generally must be filed within the later of four months from the actual U.S. filing date or sixteen months from the foreign filing date. The certified-copy rules use a similar default period, subject to specific exceptions, including the priority-document-exchange provisions of 37 C.F.R. § 1.55(i). 35 U.S.C. § 119(b); 37 C.F.R. § 1.55(d), (f), (i) (2026).

Under the DAS exception, the USPTO may receive the electronic copy during the pendency of the application and before the patent is granted. That flexibility should not become a docketing strategy. Until the copy is in the record, the application lacks the document needed to complete the foreign-priority record. Late retrieval can also create problems after payment of the issue fee, and an inaccurate priority claim may require petition practice rather than a simple code correction. MPEP §§ 214-215.02(a) (9th ed. Rev. 01.2024, Nov. 2024).

The practical rule is uncomplicated: provide the DAS code with the original ADS, inspect the filing receipt, and confirm that the retrieved document actually appears in Patent Center. The USPTO expressly places ultimate responsibility for the priority document on the applicant even when electronic retrieval has been requested.

DAS in PCT Practice

 

Three Routes Under PCT Rule 17.1

 

PCT Rule 17.1 provides three principal ways to satisfy the priority-document requirement. The applicant may submit a certified copy to the receiving Office or International Bureau under Rule 17.1(a); request the receiving Office to prepare and transmit a document that office issued under Rule 17.1(b); or request the International Bureau to retrieve a document available from a digital library under Rule 17.1(b-bis). Regulations Under the Patent Cooperation Treaty r. 17.1(a)-(b-bis) (as in force Jan. 1, 2026).

Under Rule 17.1(a), the applicant ordinarily furnishes the certified copy within sixteen months from the priority date, although a copy received after that period is deemed timely if it reaches the International Bureau before international publication. A Rule 17.1(b) request to the receiving Office also generally must be made within sixteen months. Rule 17.1(b-bis), by contrast, is not formally a sixteen-month deadline, and early publication shortens the practical window. For the DAS route, counsel should ensure before international publication both that the priority document is held in a qualifying digital library from which it is available to the International Bureau, including any required authorization, and that the International Bureau has received a valid retrieval request identifying the document and including any required access code. The best practice is to include the DAS indication and code in Box VI of Form PCT/RO/101 at filing. Regulations Under the Patent Cooperation Treaty r. 17.1(b-bis); PCT Administrative Instructions §§ 715(a), 716(a) (as in force Jan. 1, 2026).

If the code was not available when the PCT application was filed, the applicant may later provide the DAS information through ePCT's 'Obtain priority document from DAS' action. Successful retrieval is confirmed on Form PCT/IB/304. Counsel should not treat the publication date as a target date: the depositing office may need time to register the earlier application, and a mismatch in the office code, application number, or filing date can cause retrieval to fail. World Intell. Prop. Org., PCT Newsletter, Practical Advice (Dec. 2019).

A limited cure applies when a formally proper Rule 17.1(b-bis) request identifies a document considered available from a digital library but the International Bureau cannot obtain it. In that circumstance, Administrative Instructions § 716 requires notice and at least two months—or the Rule 17.1(a) period, if later—to furnish the copy or make it available. This is targeted notice-and-cure treatment, not a general extension for an omitted or defective DAS request. PCT Administrative Instructions § 716(b) (as in force Jan. 1, 2026).

Failure to satisfy the international-phase priority-document requirement does not necessarily extinguish priority in every designated State. Under Rule 17.1(c), a designated Office must provide a reasonable opportunity to furnish the priority document before disregarding the priority claim on that ground. Rule 17.1(d) prevents that Office from disregarding the priority claim under paragraph (c) where the earlier application was filed with it in its capacity as a national Office or the priority document is available to it from a qualifying digital library. These safeguards address the priority-document requirement; they neither cure an independent defect in the priority claim nor establish substantive entitlement to priority, and they should not be treated as a reason to defer international-phase compliance. Regulations Under the Patent Cooperation Treaty r. 17.1(c)-(d); PCT Administrative Instructions § 715(a) (as in force Jan. 1, 2026).

The RO/US Distinction

 

When a PCT application filed with the USPTO as receiving Office claims priority to an earlier U.S. application, the applicant may check the appropriate item in Box VI and ask RO/US to prepare and transmit the certified copy under Rule 17.1(b). That service is separate from DAS. Alternatively, the International Bureau may retrieve an authorized U.S. priority application through DAS, regardless of the receiving Office selected, when the request and four-digit code are properly supplied.

A different limitation applies when the PCT application filed at RO/US is itself intended to serve as a priority document for a later filing. The USPTO states that an authorization to permit DAS access is not recorded in an international application filed with RO/US, so counsel must use an available alternative method for transmitting that priority document. This is another reason to identify the intended priority chain before filing.

National-Phase Consequences

 

When the priority-document requirement has been satisfied during the international phase, a designated Office should obtain the priority document through the International Bureau rather than require the applicant to furnish it again. National-phase counsel should verify the International Bureau's record and the receiving national office's acknowledgment rather than assume that the international-stage request succeeded. A copy obtained by national counsel for counsel's own file is different from a further copy demanded by the national patent office. Regulations Under the Patent Cooperation Treaty r. 17.2(a) (as in force Jan. 1, 2026).

A translation of the priority document may nevertheless be required in the limited circumstances permitted by Rule 51bis.1(e): when the validity of the priority claim is relevant to patentability, or in specified cases involving an element or part incorporated by reference. Where such a translation is properly required, the Office may request a simple photocopy to accompany it. Neither step is a renewed demand for the certified priority document that the Office should obtain through the International Bureau. Regulations Under the Patent Cooperation Treaty r. 51bis.1(e) (as in force Jan. 1, 2026); World Intell. Prop. Org., PCT Applicant's Guide—National Phase ¶¶ 5.009-.010 (Sept. 4, 2025).

DAS Practice Before CNIPA

 

CNIPA as Both Depositing and Accessing Office

 

The China National Intellectual Property Administration has participated in WIPO DAS since March 1, 2012 and currently acts as both a depositing and an accessing office. WIPO's current profile identifies CNIPA as a depositing office for Chinese invention, utility model, and industrial design applications, as well as certain PCT international applications. As an accessing office, CNIPA retrieves eligible national patent, utility model, and industrial design applications and Hague international design applications. World Intell. Prop. Org., WIPO DAS: Participating Offices (last visited Sept. 5, 2026).

That asymmetry matters. WIPO's profile does not presently list foreign PCT international applications among the document categories CNIPA retrieves as an accessing office. Counsel therefore should not assume that every PCT priority document can be pulled into a direct Chinese filing through DAS merely because CNIPA can deposit certain PCT applications. The current profiles of both offices should be checked for the precise filing route.

Using a Chinese Application as the Priority Filing

 

A Chinese filing does not become useful abroad through DAS merely because CNIPA assigned it an application number. The applicant or its Chinese patent agency should submit an electronic deposit request asking CNIPA to prepare the priority document and place it in the DAS library. CNIPA distinguishes that deposit request from a retrieval request, which is used when CNIPA is asked to obtain a foreign priority document.

CNIPA's published guidance states that DAS requests are submitted electronically. After a successful deposit, CNIPA provides access to the code through its online patent-services system; the confirmation email reports the result but does not contain the code itself. A CNIPA-issued code ordinarily contains four to ten numbers or a combination of numbers and letters. China Nat'l Intell. Prop. Admin., Practical Knowledge on Electronic Exchange of Patent Priority Documents (June 5, 2020).

Once issued, the Chinese code should be sent to foreign counsel together with the office code CN, the exact Chinese application number, and the filing date. For USPTO retrieval, the recommended Chinese formats distinguish invention applications (YYYY1NNNNNNN.X), utility models (YYYY2NNNNNNN.X), and design applications (YYYY3NNNNNNN.X). Punctuation, check digits, and office codes should be copied from the official record rather than retyped from memory.

China's Confidentiality Review Is Separate

 

The most consequential China-specific point is not the code itself. Article 19 of the Chinese Patent Law requires an entity or individual intending to file abroad for an invention or utility model accomplished in China to request a confidentiality examination from CNIPA in advance. The requirement turns on where the inventive work was accomplished, not simply on the applicant's nationality. A foreign filing made in violation of Article 19 can prevent grant of a Chinese patent for the invention or utility model. Patent Law of the People's Republic of China art. 19 (promulgated Mar. 12, 1984, amended Oct. 17, 2020, effective June 1, 2021) (China).

DAS does not perform or replace that review. CNIPA's original DAS announcement linked the availability of the deposit service for Chinese invention and utility model applications to completion of the required confidentiality review. A China-originating filing plan should therefore docket three separate events: the confidentiality review, the Paris Convention or PCT filing deadline, and the DAS deposit and retrieval process.

The confidentiality-review obligation does not apply to designs. For an invention or utility model, filing a PCT application with CNIPA as receiving Office is deemed to include the review request; filing an ordinary Chinese national application, standing alone, is not. The review therefore must be analyzed separately whenever the subject matter was substantively accomplished in China. Implementing Regulations of the Patent Law of the People's Republic of China rr. 8-9 (amended Dec. 11, 2023) (China).

Claiming Foreign Priority in a Chinese Application

 

The Chinese priority claim and the priority document remain separate formalities. Under Article 29, the ordinary foreign-priority period is twelve months for inventions and utility models and six months for designs. Under Article 30, the applicant must make the written priority declaration when the Chinese application is filed. For an invention or utility model, the copy of the first-filed application must be furnished within sixteen months from the first filing date. For a design, the copy must be furnished within three months after filing the Chinese design application. Patent Law of the People's Republic of China arts. 29-30 (promulgated Mar. 12, 1984, amended Oct. 17, 2020, effective June 1, 2021) (China).

To use DAS, the foreign depositing office must first make the earlier application available and issue or activate the corresponding code. Chinese counsel then submits a retrieval request identifying the foreign office, filing date, application number, and code. CNIPA's governing announcement provides that a document successfully obtained through DAS is treated as satisfying the applicant's obligation to submit the priority-application copy under Article 30. State Intell. Prop. Off. of the People's Republic of China, Announcement No. 169 (Feb. 20, 2012).

For an unpublished U.S. application used as the priority basis, Chinese counsel ordinarily needs the office code US, the U.S. application number, filing date, and four-digit confirmation number. U.S. counsel must separately confirm that the original ADS authorized access or that PTO/SB/39 was filed. Supplying the correct number without USPTO access authorization will not allow CNIPA to retrieve the document.

Corrections and Retrieval Failures in China

 

China's revised Implementing Regulations create two limited priority remedies for inventions and utility models. Rule 36 permits restoration, for a justified reason, during the two months after expiration of the twelve-month priority period. Rule 37 permits an applicant that made at least one priority claim at filing to add or correct a claim by the later of sixteen months from the priority date or four months from the Chinese filing date. Neither remedy applies to designs, and neither should be treated as a general DAS extension. Implementing Regulations of the Patent Law of the People's Republic of China rr. 36-37 (amended Dec. 11, 2023) (China).

If CNIPA cannot retrieve the document, counsel should immediately verify the office code, application-number format, filing date, code, and deposit status. Depending on the remaining time, the applicant may need to correct the request, file a new request, or submit a conventional certified copy. Announcement No. 169 provides limited relief where the applicant completed the necessary acts but retrieval failed because of a DAS system malfunction; even then, the applicant must submit the earlier-application copy within two months after receiving the relevant notice. That is narrow system-failure relief, not a general grace period. Preserving confirmations and error notices is essential. State Intell. Prop. Off. of the People's Republic of China, Announcement No. 169, pt. II(5) (Feb. 20, 2012).

China and the PCT National Phase

 

For a PCT application claiming priority to a Chinese national application, the applicant may ask the International Bureau to retrieve the Chinese document through DAS after CNIPA has deposited it. If CNIPA acts as the receiving Office and issued the priority document, the Rule 17.1(b) transmission route may also be available.

On entry into the Chinese national phase, the priority-document question ordinarily should have been resolved in the international phase. A priority claim that remains valid is treated as the Article 30 declaration, and a priority document furnished under PCT Rule 17 need not be resubmitted to CNIPA. If the copy was not furnished internationally, CNIPA may invite the applicant to supply it within a specified period. Counsel should confirm the international record rather than initiating an unrelated DAS process; priority restoration, if needed, has its own two-month national-entry procedure. Implementing Regulations of the Patent Law of the People's Republic of China rr. 127-128 (amended Dec. 11, 2023) (China).

Special Situations That Deserve Separate Attention

 

Multiple Priority Applications

 

Each earlier application ordinarily has its own DAS code and its own bibliographic record. A later application claiming three priority dates may therefore require three separate deposits, three codes, and three successful retrievals. The fact that the applications belong to one family does not merge their certified-copy requirements.

Hague International Designs

 

Hague practice uses specialized office codes and application-number formats. For USPTO retrieval of a Hague priority application, the International Bureau supplies the DAS code, and use of the international registration number alone may not support retrieval. CNIPA's current WIPO profile identifies Hague international applications as an accessing category for Chinese design filings. Design counsel should verify the exact filing identifier, office code, and three-month Chinese document deadline.

Nonparticipating Offices and Ineligible Documents

 

DAS cannot be assumed merely because both countries participate in WIPO programs generally. If the first office does not deposit the relevant document type, or the second office does not retrieve it, the applicant must use a permitted alternative such as a conventional certified copy. The eligibility analysis should be performed when the filing plan is created, not when a missing-document notice arrives.

Conclusion

 

WIPO DAS is a valuable filing tool because it replaces repeated paper-certified-copy transactions with a secure office-to-office exchange. But the code is only one component of the priority record. The claim must be timely and accurate; the first office must make the correct document available; the second office must be authorized and asked to retrieve it; and counsel must verify that retrieval succeeded.

U.S. practitioners should focus on the four-digit confirmation number, access authorization, and the filing receipt. PCT practitioners should select the correct Rule 17.1 route and act before publication. In China-related matters, counsel should add CNIPA's separate deposit or retrieval request, the Article 30 document deadlines, and, for inventions or utility models accomplished in China, the Article 19 confidentiality review.

The best single practice is to docket DAS as a closed-loop process rather than a data-entry field: deposit, obtain the code, request retrieval, and confirm receipt. A code in the file is useful. A retrieved priority document in the official record is what ultimately matters.