CypherIt

Its a very simple app where you enter in a password and the text or select a file you wish to encrypt or decrypt.

You then just hit the "Encrypt" button.

To use encrypted text in another app just tap on the copy button and the encrypted text is placed in your devices clipboard for use in anther app.

To decrypt you will also need this app. Paste the encrypted text into the app or select the file, then use the same password and encryption settings that was used to encrypt the text or file, tap on the decrypt button and the text or file is decrypted.