With SealPath you can protect files with plain text and rich text formats (i.e. .txt, .rtf). To have to protect them you only need to drag & drop the text file on the specific protection box or, in the File Explorer, do "right click" over the file and select the protection you want to use.
The user receives the protected .txt or the .rtf and will be able to open it directly with SealPath Desktop or SealPath Lite. These applications include a Light Text Editor.