Gateway SX2803, Windows 7, 64 bit

Through a login error while trying to send photos, I lost my calendar and contacts.  I had backed up my contacts using CSV format to a folder.  In trying to restore my contacts the file had a 16 file extension which I cannot open.  No luck in downloading a program to open it.  I used a bitoptimizer Installer and after running the program it came up with over 4,000 items to correct so I didn't do it.  Any suggestions?