How to backup Microsoft Office?

I have a MacBook Pro running OS 10.9.1 that I bought in August of 2012. Today I've been experiencing a problem where an error message saying that Finder has quite unexpectedly repeatedly pops up upon startup. I called Apple about it; after restarting everything was fine, but they told me to back everything up in case it happens again because if it happens again I might have to wipe the computer clean and reinstall the operating system, which leads me to my actual question:

At the time I bought the computer, I was able to get a free version of Microsoft Office because my girlfriend at the time got a free download from her university so I was able to get a free version that way. I don't want to lose Office if I have to wipe the hard drive, but I also don't want to pay for it, so is there any way I can preserve the version I have?

If you have experienced the problem with Finder and have any suggestions regarding that I'd be would greatly appreciate it. Thanks everybody!

I asked this previously and it was closed due to a misunderstanding. Just to clarify, I am not asking for anyone to help me or suggest in any way anything that is remotely illegal. By saying "I don't want to pay," I am saying that I would like to keep the copy I have that I legally downloaded, not that I want somebody to help me illegally obtain a free copy. I did not obtain the current copy illegally and I am not asking for help in obtaining future copies illegally, I am asking if there are any ways to keep the current legal copy I have. Thank you, and I apologize for the previous misunderstanding.

You stated in your first post that you downloaded the copy from your girl friend's school which you are not a student at. MS Office was a free download for her, not you. So, in reality, you did not legally download it did you?

Regardless, without a legal serial number when it's moved you won't be able to activate it again. I know this is true because I recently moved my copy from one iMac to another and I had to activate it again with Microsoft. Activation requires that the serial number be entered.

There are free alternatives to MS Office: LibreOffice, OpenOffice, and if you recently purchased a new Mac, Apple will give you a copy of the latest iWork for free.