I have this but I'm on Imac OS X Snow Leopard

I am using an IMAC OS X Snow Leopard v. 10.6.8 and have a document saved in .rtf and have had it for a year now. Recently, I noticed there is another copy of it, the only difference is after the document name there is a tilde symbol right after the document name and before the .rft extension. Can anyone explain why this would suddenly appear and should I save it or delete it?