Simplifying, Textpack is a markdown file, plus optional image files, packed into single zip file.
The two-key mechanism allows you to cancel the purchase in case of a refund request.
See attached video to see how to configure email account in Keepmark.
No. Currently Keepmark is a desktop application. However, documents are stored in a user-accessible form and can be synchronized with mobile devices, e.g., using services like Drobox or the WebDav protocol.
Yes. The Trial version is limited to 20 indexed tasks and 20 indexed documents.