If I format my WD passport to FAT32, will the data currently on it be lost?


I am trying to use my WD Passport between two computers. it already has a lot of files saved from a PC.

Now I need to back-up my Mac.

If I format to FAT32 from Disc Utilities of my mac, will it format the whole thing and erase the files currently on it?


Yes you will loose your data. Check post 6 in this   http://community.wd.com/t5/WD-Portable-Drives/unwritable-drive/td-p/435872 and see if any of them will help. The down side of formatting FAT32 is the largest file size is 4 gig.