vb6 Hex or something

Ok your probably wondering whats with all the questions any yes I have searched other places before posting here. Here is my question

I have a program that generated text documents that need to be encrypted which I have done. What I want to do is have hex in the file but not viewable unless opened in a hex editor. Like some files show a bunch of dots but opened in a hex editor are each different hex codes. How would I add them to my files.

The reason I want to do this is to create a checksum to determine the authenticity of the file the program is dealing with. So someone can't just delete the file and re-make it, or edit it without the program knowing its been tampered with.