Which part of the archiving standard to claim
The archiving standard is a family, not a single rule. Four of its parts can be claimed here, ten claims between them, and choosing takes two questions.
Summary
The family is called PDF/A, and each of its members is called a part. A part is a full set of rules; a level, written as a letter after it, says how far that part goes. All of them promise the same thing first: everything the document needs to be read is inside the document.
Two questions settle the choice. Does the document have to be read out loud by screen-reading software, or its text extracted in reading order, paragraph by paragraph? Then it needs the level that carries the structure of its own text. Does it have to carry another file inside it — the data of an invoice, a spreadsheet, a photograph? Then it needs a part that allows that.
If neither question applies, take the plainest claim: the page will look the same for as long as the file exists.
Technically
Parts 3 and 4 define six claims between them, and the engine writes five: part 3 at level B, part 3 at level U, part 3 at level A, part 4, and part 4 at the level that carries files. The sixth, PDF/A-4E, the level of part 4 for engineering documents, is planned for a future version. Part 3 rests on PDF 1.7 and part 4 on PDF 2.0, and the claim settles the version rather than following it: a document whose version and claim disagree is refused before a byte is written.
Level A of part 3 asks for a structure tree; the engine refuses to write the file without one. Part 4 drops levels A, U and B: accessibility is now a standard of its own, PDF/UA, and a document that wants both claims both. The level of part 4 that carries files asks for at least one, and the engine refuses the document that has none.
The engine writes ten claims: both levels of part 1, the three levels of part 2, the three of part 3, and both of part 4. Level B asks for the page to stay reproducible for as long as the file exists. Level U adds that every drawn character maps back to Unicode, so the text can be searched and copied. Level A adds the structure of the text and, in part 1, which has no level U, the mapping back to Unicode and the language of the text. In a request to the service, the archive key takes one of these ten names: pdfa1b, pdfa1a, pdfa2b, pdfa2u, pdfa2a, pdfa3b, pdfa3u, pdfa3a, pdfa4 and pdfa4f. What the engine writes and what a request may ask for are the same ten.
Clause by clause
Part 1 is written on PDF 1.4, the version of the format it was settled against, and a request naming it is written as that version and no other. It is the strictest of the parts: a document claiming it is refused if it uses transparency, if it holds a layer, or if it carries a file.
What the engine does on its own
The engine does all of this as soon as a document claims the standard, whatever else the calling program asks for.
- Writes the claim into the document's own description: the part, the level where the part has one, and the year of the edition.
- Refuses the document when the PDF version and the claimed part disagree, naming both.
- Writes no document information dictionary under part 4: the title, the author and the other entries live only in the description packet.
What you supply
The engine states what it was given and invents nothing else: without those values it refuses the document rather than choosing one for you.
- The claim itself: no document claims a standard by accident.
- The PDF version that goes with the part: 1.7 for part 3, 2.0 for part 4.
- A structure tree, for level A of part 3, and at least one carried file, for the level of part 4 that carries them.
The published texts behind these rules
| Published text | What it asks for |
|---|---|
ISO 19005-3 6.1.2 |
The version the file header names is the one the part rests on. |
ISO 19005-4 6.1.2 |
The same, for the part built on PDF 2.0. |
ISO 19005-4 6.1.3 |
Under part 4, a document says what it is in its metadata packet and nowhere else: it carries no information dictionary at all. |
ISO 19005-3 6.7.3.3 |
A document at level A carries a structure tree. |
ISO 19005-4 6.9 |
A document claiming PDF/A-4F names the files it carries. |
The other families of requirements
Every font the document uses is embedded in the file Colours that mean the same thing on every device A page that comes out the same for everyone The document says what its marks stand for A document that carries other files inside it What the file says about itself Checking the claim, before and after