We had a similar problem in WeasyPrint: cairo produces the PDF files but does not support bookmarks/outlines or hyperlinks. In the end we bit the bullet, read the PDF spec, and did it ourselves.
WeasyPrint’s pdf.py has a simple PDF parser and writer that can add/override PDF "objects" to an existing documents. It uses the PDF "update" mechanism and only append at the end of the file.
This module was made for internal use only but I’m open to refactoring it to make it easier to use in other projects.
However the parser takes a few shortcuts and can not parse all valid PDF files. It may need to be adapted if PyPDF’s output is not as nice as cairo’s. From the module’s docstring:
Rather than trying to parse any valid PDF, we make some assumptions
that hold for cairo in order to simplify the code:
- All newlines are '\n', not '\r' or '\r\n'
- Except for number 0 (which is always free) there is no "free" object.
- Most white space separators are made of a single 0x20 space.
- Indirect dictionary objects do not contain '>>' at the start of a line except to mark the end of the object, followed by 'endobj'. (In
other words, '>>' markers for sub-dictionaries are indented.)
- The Page Tree is flat: all kids of the root page node are page objects, not page tree nodes.