why won't my microsoft word mac document open on with microsft pc?

Hello,
I have the new microsoft office - microsoft word x and have tried to open it on my pc. The file would not register. Do you know why?
I thought microsoft documents would be readable by microsoft on either platform.
I also have tried saving the document at an older microsoft word format.
Any ideas why?
thanks,
M

Have you checked the 'append file extension' box in the save dialogue?

If not, select the document and rename it to "documentname.doc" and see if it'll open then...

This shouldn't be an issue at all, I haven't find a document file that I couldn't be opened, which are compatible with Word on both mac and pc. What software title are you using to open the document and what exactly does it say on Windows, when you try to open it? Also, crtl-click on the document on your mac, then Open With, and see if you can open it with other apps on your computer.

And when you go to "Save As" in Word on the mac, before you click "Save", click on "Compatibility Report...", and see what it says.

How old is the version of Word on the PC?