> $ sudo apt install ./master-pdf-editor-4.3.89_qt5.x86_64.deb
> ./master-pdf-editor-5.7.08-qt5_included.x86_64.deb
> Reading package lists... Done
> Building dependency tree
> Reading state information... Done
> Note, selecting 'master-pdf-editor' instead of
> './master-pdf-editor-4.3.89_qt5.x86_64.deb'
> Note, selecting 'master-pdf-editor' instead of
> './master-pdf-editor-5.7.08-qt5_included.x86_64.deb'
> master-pdf-editor is already the newest version (4.3.89-2).
> The following packages will be upgraded:
> master-pdf-editor
I suggest you look inside those .deb files: they seem to both name the
package they install `master-pdf-editor` but dpkg does not allow
installing different versions of a given package at the same time.
So you'll need to edit those `.deb` to change the package name from
`master-pdf-editor` to (say) `master-pdf-editor4` and
`master-pdf-editor5`, for example.
Stefan "who does that kind of thing in order to install emacs25,
emacs26, and emacs27 at the same time"
