My 2009 macbook microsoft word documents are not being accepted as files.

My 2009 Macbook seems to be falling behind. Using Mac OS X (Version 10.6.8) and Microsoft Word for Mac 2008 (version 12.3.6).

For some reason, my files do not work online. They are "invalid." For example, "invalid file type" popped up on my school online dropbox and my online grad school application. My files are, however, in the correct (doc, docx, pdf) file types. I had to go on campus and use a PC to upload assignments and applications.
Not sure if it's my software or old word version.
Anywho, I just need some answers! 🙂