Encrypt your personal data without any application/softwares. In this instructable we are going to rename the extension of the file. Then the system will assume it as unknown file type. This trick will Works in all platforms.
Step 1: Select Your Files and Rename the Extension
Using file Explorer in my android phone. I renamed the extension of "file.txt" to "file.mp". (use can other extensions mp3,png ,rar etc ) Then the system will assume it as unidentified file. We can open it by renaming to original extension or by using "open as" option. For large number of files we can use ES file Explorer since it has batch renaming option.
Step 2: For Windows
In Windows->open the Explorer ->view option -> select file name extention.
Hint:Remember the original file extension.