You are having problems with ligatures. Make sure the the fonts are embedded in the PDF file. Choose the Advanced tab in the second export dialog window and make sure the Font subsetting is set to 0%.
Thank you Larry, it's much appreciated.
If you are exporting the PDF from ID the ligatures should be embedded automatically unless for some reason you are using an old "expert" font for the ligatures and the font isrestricted. You would only have a problem with that if you were printing to Postscript and disitilling or using the Save as PDF in Apple's system.
I suspect the problem is really with the viewer being used and you should suggest that the recipient download and install the free Adobe Reader.
Thank you Peter. I don't know what the view was using to read the PDF, too late to ask them. I sent them the same file but zipped it before emailing, and when they openned the zip file, there were no holes in the PDF file. I don't know what that means, but I have a theory that emailing corrupted the original PDF file, and zipping it protected it from that happening...
p.s. Sorry for the late response on this thread.