I do a lot of work with PDFs at my job. ImageMagick is, by the
assertion of its own developers, non-ideal for most PDF work because
it is meant for Images and most PDFs have embedded text, postscript
vectors, bookmarks, and all manner of metadata that you probably want
to keep and/or keep lossless.
pdf-stapler is very close to being a proper replacement.
https://github.com/hellerbarde/stapler
It does all the concatenating and rotating and retaining-of-data stuff
that pdftk does.
It doesn't have a very robust system for dealing with bookmarks and
other metadata.
I coasted with pdf-stapler for a while, until I needed to do some
serious PDF editing, at which point I installed Snapcraft (on fedora!)
and then installed pdftk as a snap. Works like a charm, highlly
recommended. Here are notes on how the Snap install goes on fedora:
https://github.com/smoser/pdftk/issues/6