Be aware, that you only are legally allowed to do that, if the font's license does not forbid it. Here is a way to extract an embedded font from a PDF using Free Software. I only know of two commercial products which do that: 's pdfToolbox4 and Enfocus' PitStop (of course, there surely are others, but I'm not aware of them, and these two are the market leaders here). I'm not aware of any free-as-in-speech (GPL-licensed) or free-as-in-beer (gratis) software that could probably do that (by un-embedding the font first, and then re-embed a sustitute font). It is extremely difficult to replace a font that is embedded into a PDF.

I would be interested in other free software PDF editing tools ( whether zero-price or not), if they'll help with this task.

Emacs (or any text editor) for editing the PDF code.

Evince (and I also tried Okular) for viewing.

If someone can tell me how to take a font from one PDF and substitute it into an existing PDF, that would be a solution. I also have another similar document using Caliban, which does display properly including the glyphs that are listed above as broken. The glyphs that display blank include “i”, “T”, “V” perhaps others that I haven't discovered. The font in question is Adobe's Caliban Regular, which I can see embedded in the document.

How can I modify the PDF document - I have no access to the source document used to create it - to substitute a different font in place of the broken one? However, the font for those fields is broken: it is missing some glyphs, so when I enter text some gaps appear. I have a PDF document (not encrypted) with editable form fields.

Enfocus pitstop pro 13 license broken