Using the QPDF AppImage bundle (for Linux x86_64 systems only)

First advice:

After downloading, you have to set the executable bit for any AppImage (for security reasons this is disabled by default): chmod +x <name-of-application>.AppImage
Run the QPDF AppImage with the '--usage' parameter to start learning some useful details about built-in features of this specific AppImage.

More tips:

You can rename the AppImage to any name allowed for file names on Linux. The '.AppImage' suffix is not required for it to function. It will also work as expected if you invoke it from a symlink. Using 'qpdf' as its filename or symlink name is OK. However, you may want to continue using the QPDF package provided by your system's package manager side by side with the AppImage bundle: in this case it is recommended to use 'qpdf.ai' as a short name for (or as the symlink name to) the qpdf-.AppImage.
[...more tips to come... work in progress...]