Program to encrypt a file so that it is safe to email [closed]
Use 7-Zip to encrypt into a zip file, using AES encryption, and you're all set.
You can use PGP to encrypt your mail and you can add a signature. It's a everyday plus !
Truecrypt is my favourite way of encrypting sensitive data. As well as encrypting files, it can also encrypt drives (perfect for carrying stuff around on a USB stick). The program works on Windows, Mac and Linux too.