Comment by hnick

My weirdest that I can recall right now was a PDF file that would not print. Since the printer was typically unhelpful with the error message, as was support (this is a room-sized commercial printer but we didn't get the help I'd really expect), I had to dive into it myself.

Long story short, whatever had produced the PDF had also embedded a TrueType font where one character was named //something. This is fine. The character just has a weird name, but it works. It's technically up to spec AFAIK, and I got it out of the PDF with ttfdump to have a look at it.

Well the printer's internal RIP, unknown to us, converted the PDF to Postscript when rasterising. And //something is called an "immediately evaluated name" which I forget the details for, but basically this font character, interpreted as postscript, was causing a lookup for a named variable which did not exist. Hence the crash.

I had a similar one where Adobe InDesign had been used to make a PDF where someone had selected the words to change the font, but not the spaces between (or perhaps they did, and it was a bug). This meant that the PDF included a subset font that only included the space character. Since the space character is not drawn, this resulted in a 0 byte long glyf table. Based on my reading of the TrueType font spec at the time, this isn't really proper.

Printer didn't like that one bit and died as it does to anything that smells slightly wrong. Adobe said it was fine and up to spec though, apparently 'TrueType' has a different meaning inside a PDF :)