Encrypt any text (100-200 words, any algorithm is fine but provide evidence that it woks)

Firstly we need to add our file which we want to encrypt:

Next program will show us this text in file and count of words:

To encrypt this text we need to point out key, when the key changes, our text is always encrypted differently:

After this we indicate to encrypt our file and it will encrypt the file and save it to another txt file: