That suggests one of three things:
1. The "documents created by another user" are corrupt;
2. Your client's Office installation is faulty; or
3. The "documents created by another user" use fonts that are not installed on your client's system.

You need to narrow down the problem.

Does your client have problems with all documents, or only "documents created by another user"?

If it affects all documents, the problem lies with your client's system and the first thing to do would be to repair the Office installation.

If it affects only "documents created by another user", do the documents contain only the standard Windows/Office fonts (e.g. are those fonts installed on both systems)? If not, have the user either revert to the standard Windows/Office fonts or at least embed the fonts in the documents (font license permitting).

If the "documents created by another user" contain only the standard Windows/Office fonts, those documents may have acquired some form of corruption. Corrupt documents can often be 'repaired' by inserting a new, empty, paragraph at the very end, copying everything except that new paragraph to a new document based on the same template (headers & footers may need to be copied separately), closing the old document and saving the new one over it. Obviously, this is best done at the source. And, if the corrupt documents are all based on the same template, that template may be the source of the corruption, in which case it, too, needs to go through the above repair process.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]