Does the string <!-FTCACHE-1-> in a PDF file mean anything?

Question

My program downloads a PDF file from a source location every day. When I see the binary text of the PDF file in Notepad, I find that sometimes the PDF file has the string <!-FTCACHE-1-> at the end. Sometimes this word is missing from the PDF file.

My program downloads this PDF daily and compares it with the previous day's PDF file using the Windiff binary comparison.

99% of the time, Windiff reports differences in the PDF file just because one PDF contains the string <!-FTCACHE-1-> at the end.

Does anyone knows what the reason behind this is?

Thanks, Praveen

Answer 1

"FT" could be FreeType, the open source font engine. The comment probably comes from the software that generates the PDF. If you can somehow identify that, you could (assuming it is open source) perhaps take a look through it and see what causes it to emit the comment.

FreeType has a source folder dedicated to caching, the root source file there is called ftcache.c. It doesn't do a lot though, just #includes (!) the other source files.

Googling on the string you see, reveals several more or less random PDF:s that seem to contain it.