You canât. Fixed-size compression is almost impossible in lossless mode and very hard in lossy mode, and PDFs may be a combination of both, with emphasis on the lossless side. Add to this this the âany PDF fileâ constraint and you have the impossible.
The same has been said for PDFs a million times: PDF files are not real files: a format is a specification, whether you use X11, Windows-based or Unix-based fonts. The point of a PDF is to give you the option of a certain level of information. There are all sorts of PDFs, most of which are useless. I suggest you get a copy of your favorite software.