Not able to print all letters in a sentence/paragraph

We have been having some problems printing some of our leaflets/posters. They are PDFs and are opened and printed with Adobe Acrobat Reader.

We have a non-standard/personalised font that we use in these documents that does not print correctly. It displays fine in the reader, but some letters are not printed.

Previously I had "printed" the document to PDF which worked correctly and flattened the original document that then prints correctly. It only seems to affect this font (every other font prints correctly) and seems to be in a variety of documents.

Any suggestions?