[TYPO3] Front End User Registration; image field

[Tesori Musicali Toscani]

Hi,
may I put in Front End User Registration in the field "image" a PDF?
my be by changing the type of "image" into the table fe_users table  
in blob instead of tinyblob?
I notice that I can, I tried and I could... but the question is:  
could I have problems that I don't notice?
why to call that field "image" and not "file"?

I hope I was clear,
thanks
laura