The notes a program leaves in the file for itself
Leave data in the document for the program that wrote it, filed under that program's name and dated. No reading software shows it.
Summary
A press room sends a proof out and gets it back three days later. To pick the job up it has to know which run the sheet belongs to — and that is nothing the person holding the sheet should be shown. So it travels under the document instead of on it. What you leave is filed under the name of your own program, so two programs leaving notes in the same file never read each other's, and it is stamped with the moment your program last touched it. Nothing of it is drawn, and it rides along with the file wherever the file goes.
Technically
Written at the top level of a request, under
"private_data"
private_data writes the /PieceInfo of the document catalogue and the /LastModified beside it, under the private name program states. What private holds is a string the caller composes, and the service writes it as given: nothing here reads it, parses it or holds it to a shape. A page carries its own through page_private_data, and a named drawing through drawings[].private_data, each filed under its own program the same way. A piece is PDF 1.3 on a page and 1.4 on the catalogue, so this raises the version the document announces no higher than the library already writes.
Request schema
-
private_data— object, optional, absent leaves no piece at all. -
private_data.program— string, required. The name your data is filed under, and what keeps two programs from treading on each other. -
private_data.modified— string, required, an ISO 8601 timestamp. When your program last changed what it left. -
private_data.private— string, required. The data itself, as your program composed it. It is written as given.
Scope: the whole document. page_private_data leaves the same on one page, and drawings[].private_data on a named drawing.
A whole request that creates a PDF
{
"private_data": {
"program": "PressDesk",
"modified": "2026-09-07T08:15:00+02:00",
"private": "{\"run\":47,\"press\":\"K4\",\"proof\":3}"
},
"standard_fonts": [{ "name": "sans", "face": "helvetica" }],
"items": [
{
"type": "text",
"rect": { "llx": 72, "lly": 700, "urx": 523, "ury": 740 },
"content": ["A proof, and the run it belongs to underneath it"],
"font": "sans",
"font_size": 12
}
]
}The document as a whole
The numbers reading software shows A hundred letters in a single file What the document says about itself The notes a program leaves on one page A file still readable decades from now The print standard the document claims The password that opens it, and what may be done with it An invoice a person and a machine both read The address relative links are read against The PDF version the file declares What a picture says about itself, and how it is read The attachments the document carries beside its pages The carried files shown as a portfolio Which attachments a page claims The identity card a single page carries The accessibility standard the document claims The standards the finished document is measured against
Where to go next
Every JSON key of a request, in one page The other forty-one settings of a request