Why are files corrupted?

Hi,
My partner has a mac. She has never looked at any let's say 'dubious' sites or anything like that, yet it appears that despite Macs reputation, she has some sort of virus on her Mac.
This issue is thus: if she creates Word or PowerPoint files etc on her Mac, is she opens these files on any other computer (PC), they are corrupted and do not work.
So far I have managed to determine that there are no Mac virus' as such, but Mac stores them and passes them on to PCs. Is my understanding correct?
Also, does anyone know of any software that can just eliminate this problem - ie completely clean up her computer?
I would be most grateful for any help.
thanks in advance,
Sandown

what version of office is she using?

your best bet is to download ONYX and run most of its clean up and repair services.

Then download ClamX to scan for any PC viruses that may have gotton on to her mac

Hi,
Thanks very much for your response. Im not sure which version it is but I think it is very new.
I will look into this software. Thanks again.