Our tool uses AES-256 encryption algorithm on both macOS and Windows. However, the output file has indeed our file extension.
The tool creates a copy of the file and encrypts this copy using the AES-256 algorithm, so that you can securely share it. The original file is still kept on your computer. It is up to you what to do with the original.
If you want encryption on the system level, there is a build-in macOS application "Disk Utility", which provides such functionality.