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: