Axantum Software - (Free)
AxCrypt is a tool that covers the need of security by encrypting any document desired.
AxCrypt is a software utility specially designed for data encryption. Using the application is very simple since it is directly accessible from the context menu in Windows Explorer by just selecting a folder or file, and then entering a custom encryption key.
When it is needed to consult a document, the authentication key is required. If there are changes made to the file, it is automatically encrypted again. Similarly, temporary files are permanently deleted from the hard drive without a recovery is possible later. Encryption is done with a 128-bit key, which makes it impossible for hackers. It is imperative that the password to open a file, otherwise it is impossible. For editing an encrypted file, simply double-click it.
It is able to encrypt files that are more than 4 Gb, except for those who are self-extracting.
AxCrypt also includes many other features such as administration from the command line or the compression before encryption.