PDF 1.7 and PDF 2.0 are two editions of one format. PDF 1.7 became the international standard ISO 32000-1 in 2008; PDF 2.0 is ISO 32000-2, first published in July 2017 and revised in December 2020. A file declares its version in its first bytes, %PDF-1.7 or %PDF-2.0. For reading and printing the difference rarely shows, because new features are designed so that older readers can skip them.

What changed in PDF 2.0?

The Library of Congress’s description of the format lists the main changes:

  • Text strings such as a title or a bookmark may be UTF-8 as well as PDFDocEncoding or UTF-16.
  • Encryption: weaker schemes are deprecated, and “Only AES-256 encryption used in a secure encryption scheme is encouraged in PDF 2.0.”
  • Signatures follow the PAdES standard, with “New structures” for “long-term validation of signatures.”
  • Print: output intents per page instead of one for the whole file.
  • Associated files, first defined by PDF/A-3, tie attachments to the document, a page or a part of it.
  • Tagged PDF gets new structure types, in a namespace of their own.
  • Dropped or deprecated: XFA forms, the Movie and Sound annotations, and every document information entry except CreationDate and ModDate.

Where is a PDF’s version written?

In the first line of the file and, from PDF 1.4 on, optionally in the document catalog’s /Version entry, which “if present, shall be used instead of the version specified in the Header.” That lets an appended save raise the version without rewriting the first line. A stock Mac shows the version Spotlight recorded with mdls; Poppler’s pdfinfo (brew install poppler) reads it from the file:

$ mdls -name kMDItemVersion "Demo Invoice.pdf"
kMDItemVersion = "1.3"
$ pdfinfo "Demo Invoice.pdf" | grep "PDF version"
PDF version:     1.3
$ head -c 8 "Demo Invoice.pdf"
%PDF-1.3

All six demo documents made for PDF Textfix’s screenshots were drawn with Quartz, the PDF writer in macOS, and declare 1.3, with no /Version in their catalogs.

What did each PDF version add?

Version Examples of what it brought
1.2 Linearization, for fast web viewing
1.3 The euro sign in the standard Latin character set
1.4 Transparency, and the catalog’s /Version entry
1.5 Object streams, many small objects compressed together
1.6 AES encryption
1.7 Portable collections (PDF Portfolios) and an extension mechanism; ISO 32000-1 in 2008
2.0 UTF-8 text strings, AES-256 encouraged, PAdES signatures, per-page output intents; ISO 32000-2

Why does a viewer rarely care about the version?

The standard says new features “can safely be ignored by a conforming reader that does not understand them.” The version matters where software rejects files, such as an upload form that accepts some versions only, and in PDF/A: PDF/A-1 builds on PDF 1.4, PDF/A-2 and PDF/A-3 on PDF 1.7, and PDF/A-4 on PDF 2.0.

Does editing a PDF change its version?

That depends on the writer. qpdf keeps a file’s version unless a feature it adds needs a newer one, raising it only “as needed when adding features that require newer PDF readers.” PDF Textfix’s Save writes through qpdf, keeps object streams as they were and adds no encryption, so the version stays as declared; the demo invoice rewritten with the same qpdf settings still begins %PDF-1.3. Saving with no edit writes the file back byte for byte. Other editors may write their own default, so check the header after saving.

Questions about PDF versions

Should I save as PDF 1.7 or PDF 2.0?

If a portal, printer or archive names a version, use it. Otherwise choose 2.0 when you need one of its changes, such as PAdES signatures or per-page output intents; for reading alone, the difference rarely shows.

How do I change the version of a PDF?

qpdf’s --min-version raises a lower version and leaves a higher one. --force-version sets an exact one, but forcing a lower version “will cause qpdf to disable certain features of the document.”

Is PDF/A a version of PDF?

No. It is an archival standard built on a PDF version, with extra rules; see PDF/A.