A free program for Android, by MobilDev.

Encrypt File Free is a simple, easy-to-use application that helps you encrypt and lock your photos, videos, audio, pictures, documents, and other files.

The app supports the following file formats:

JPG

PNG

BMP

TIFF

GIF

TGA

AVI

MOV

MP4

WMV

WMA

Audio

MP3

M4A

M4V

M4B

Wav

Mpeg

Mpg

XLS

PDF

DOC

PPT

XLSX

Text

The app can be used in the following ways:

Automatic: You can set a password and use that password to encrypt all the files that you choose. This mode is useful if you don’t know the password or if you want to make sure that all your files are protected.

Manual: You need to enter a password to encrypt each file.