Start by checking to see if that font has been embedded in the PDF. If not then all bets are off for being able to properly process the file. Safest bet is to go back to the client and ask them for a PDF with the fonts embedded. If not, you can try to fix what you've got. My guess is that your dealing with a cross platform font issue where the glyphs for the ligatures are different in the platform or version of the font you're using.
From the File Menu choose Properties and click on the font tab. If the fonts are not listed as "embedded" or "subset embedded" that's the source of the problem. If you have the EXACT version of the missing font in question, you might be able to use other tools to embed it. You'll need to quit out of Acrobat and load the font, then re-open the file and see if the type is displaying correctly. Go back into Properties and check the font usage again, see if the font used matches the fonts that are being called for in the document. If that's the case you can use Pitstop or the Embed Fonts PDF Fixup in the built in Preflight to fully embed the font.
Shawn
