A family of Microsoft word processing software products for creating web, email, and print documents.
Your Word 2007 docs will not open in Word 2007? That is not a compatibility issue; that is an out-and-out problem.
To answer your question, however, yes, Word 2007 docs can be opened in Word 2010, though they will open in Compatibility Mode. This is primarily so that, if you make changes and save them, they can still be opened in Word 2007 with all features intact. If you save a Word 2007 document as a Word 2010 document, some features that are new in Word 2010 will become available to you, but they might create effects that Word 2007 would not be able to work with.
And no, you won't be forced to buy Office 2010 or even to use it unless your employer buys it and requires you to use it.