Oh, how to retrieve it:
For FTM
File
Open
Look in (where you saved it after it was sent to you)
enter file name
drop down to "Files of type".....Gedcom
Your program should open it.
You might have to do the same to get back to your original file, but rather than Gedcom, enter your file type. For my Family Tree Maker, I would chose "Family Tree Maker for Windows."
I remember when I first started 4 years ago, I thought the gedcom had erased my own files when I opened it. Boy did I panic until I figured out what happened. If you can't find it for some reason, use your "find" function on your computer.
By experience...be very very careful about merging. Gedcom gives you the opportunity to merge that person's work into your own. It can cause havoc...made my daddy my own cousin a number of times (because he was) as well causing a lot of other problems.