When producing the final, print-ready PDF from an Illustrator file, it’s a thoughtful gesture to convert all the text in the file to outlines (Type/Create Outlines) prior to saving it. Otherwise, when the next user opens the file in Illustrator — say, in the print shop as they ready the file for production — they’ll receive an error message about missing fonts. Unless, by some strange coincidence, they happen to have that obscure Elven font you found at DaFont already installed on their machine.

[Having spent some time working the graveyard shift at a print shop, I can tell you that the revenge for submitting files this way is printing “as-is”.]

So what does one do when on the receiving end of such a file?

Start by creating a new Illustrator file, then placing the PDF in question (File/Place) within. At this point, it will be a solid object, as though it was an image, without any option to edit the design.

Next, with the design still selected, choose “Object/Flatten Transparency" from the top menu. This will open a dialogue box of options, the most relevant of which to the matter at hand reads Convert All Text to Outlines. Select this, then click Okay. Save this as a PDF (like the original designer should have done in the first place) and proceed with your edits.