Sustainability of Digital Formats: Planning for Library of Congress Collections

PDF/A-4f is defined in ISO 19005-4: Document management — Electronic document file format for long-term preservation Part 4: Use of ISO 32000-2 (PDF/A-4) Annex A: Requirements for PDF/A with Embedded Files. Note that the PDF Association states that "a formal dated revision of PDF/A-4 is currently being prepared by ISO TC 171 SC 2 WG 5" in 2025 and errata are listed on the PDF Association's GitHub repository. PDF/A-4f is a subtype of PDF/A-4 and the specification states that "PDF/A-4f [is] a synonym for ISO 19005-4 Level F conformance." See PDF/A-4 for general file and structure information and PDF/A_family for more details on the PDF/A family of standards.

PDF/A-4f must contain an EmbeddedFiles key in the name dictionary of the document catalog dictionary. All file specification dictionaries present in the value of the EmbeddedFiles key shall comply with the requirements of , except that the embedded files may be of any type. Embedded files that do not comply with PDF/A-1, PDF/A-2 or PDF/A-4 should not be rendered by a conforming PDF/A-4f processor.  However, a conforming interactive PDF/A- 4f processor should enable the extraction of any embedded file, requiring an explicit user action to initiate the extraction. The specification notes that "The extraction process generally consists of copying the raw byte stream of the embedded file data (possibly after any decoding of filters that might be applied) from inside the PDF to some external byte storage system (e.g., disk or memory)."

To aid in transparency which is essential for digital preservation and archival purposes, a "PDF/A-4f conforming interactive processor shall provide a mechanism to display information about file specification dictionaries that include an embedded file stream but which are not listed in the EmbeddedFiles key in the name dictionary of a conforming file. In addition, a conforming interactive processor may also choose to display information from the associated embedded file stream dictionaries or their Params dictionary."

It's worth noting that PDF/A-4e files can also contain embedded files and therefore may contain an EmbeddedFiles key in the document catalog dictionary. In such cases, the file specification dictionaries present in the value of the EmbeddedFiles key must also conform to the requirements of PDF/A-4f.

Other versions of PDF/A also support embedded files. PDF/A-2 is a constrained version of ISO 32000-1 (Adobe PDF version 1.7) which supports attachments of only PDF/A files; PDF/A-3 is also a constrained version of ISO 32000-1 (Adobe PDF version 1.7) but allows embedding of files of any type, not just other PDF/A files (as permitted in PDF/A-2); PDF/A-4f is defined from ISO 32000-2 (PDF 2.0) permits embedded files of any type and as well as the additional features supported in PDF 2.0. In essence, PDF/A-4f is a successor to PDF/A-3. Dietrich von Seggern, in Callas software: Making PDF/A conversion easier, says this about use cases for PDF/A-3 vs PDF/A-4f: "From an archiving perspective, it is essential to limit the variety of file formats used; these variants therefore require a framework of additional rules. But there are striking use cases for them, that all have in common that there is a specific, defined relationship between the actual archive file and the files that are embedded within it. An example are embedded source files – say, saving a spreadsheet alongside a PDF copy, digital invoices containing machine-readable datasets embedded into a human-readable PDF/A-3 file (for example ZUGFeRD invoices). Email archiving is another classic use case for PDF/A-3 and -4f. Here, the original email can be embedded in EML or MSG format, along with attachments."

Overall adoption of PDF 2.0-based formats such as PDF/A-4f and PDF/A-4e is still emerging in the marketplace. Several platforms note support for PDF/A-4f such as iText Core/Community 9.2.0, Scanshare v5.23.10 (October 16, 2023), Power PDF and CIB pdf toolbox. Docusign in their PDF/A Conversion and Compliance (see link from navigation tree on https://support.docusign.com/) specifically states that as of July 2025, it does not support PDF/A-4f (or PDF/A-4e). See also PDF/A-4. Comments welcome.

See also PDF/A_family and PDF/A-4.

Accessibility Features

PDF/A-4f has no specific support for digital accessibility and may be further limited (or improved) by the accessibility features of the embedded files. Note that a conforming interactive PDF/A- 4f processor should enable the extraction of any embedded file and the embedded file may have different accessibility needs or support. See PDF/A-4 which recommends following the PDF/UA standard, which provides detailed guidelines and technical specifications for creating accessible tagged PDFs.