preview document files

I'm a total lay person! Just used Diskinventory and found that I have an enormous file called preview document, over 60 GB. Since it seems to me that I have these files in proper folders, and they are perhaps preview copies, I am tempted to delete them. Is is just like a log or history of opening images in Preview? Or would this action affect the original files? By the way, I only recently changed to Mac... Thank you