Why do my Office 2007 files automatically convert to 2013?

You mentioned "When [you] work in Word and save", which version of Word are you using? If you're using Word 2013 and Save it it's probably adding metadata to the file that Word 2007 can't use. From my experience, I've been able to use files created and saved in Word 2013 in Word 2007 with no issues, but there could be a technical gap now since the two versions are six years apart. Using anything earlier than Word 2007 is where I run into issues.

Do you have both versions installed on your laptop?

When I save it, I always save it as a 97-03 version as old habits die hard. I have done this with multiple documents and since the 2013 is only a trial version, I'm locked out from making any changes to the documents. It has converted all my old files automatically too. I would love to uninstall 13 but that still leaves me with the problem that my documents have been converted.

First of all, Word 2013 is capable of saving files in the older format (Save As) and I'm surprised that it's automatically saving them in another format; usually it will just save them in the original format, but I guess that's another issue.

Have you tried opening them with Word 2007? DOCX files should be backward compatible back to Word 2007, even though they were designed with Word 2013.

Uninstall the 2013 trial, after which you may have to repair 2007.

No later version of Office converts previously saved docs

http://office.microsoft.com/en-us/excel-help/repair-or-remove-office-2010-HA010357402.aspx?CTT=1

http://www.online-tech-tips.com/ms-office-tips/fix-microsoft-word-has-stopped-working/comment-page-1/#comment-83759

http://technet.microsoft.com/en-us/library/gg998767.aspx#BKMK_OfficeRepair Office 365 (2013) - Repair is same as earlier versions

http://technet.microsoft.com/en-us/library/cc178956.aspx Setup command-line options reference for Office 2013 including repair

The factory installed trial is typically called something  like “Microsoft Office 20** Single Image” because it allows the factory to install all 3 trials (Home and Student, Home and Business, and Pro) at the same time. (For this problem you can ignore Office Starter, and an entry that is just "Microsoft Office 2010")  If you are uninstalling the factory trial to clear up conflicts with another installed copy, you MUST do an Office Repair of that other installed copy, boot the computer and you will probably have to also do an activation of the installed copy.