PDF manipulation (crop, rotate, swap page order...) support
Especially useful for printing, it would be nice to have it as a feature in Evince. However, while these operations are by themselves not complex algorithms, designing something like that while keeping Evince look fully tidy definitely needs UX work. Some ideas: https://support.apple.com/en-gb/guide/preview/crop-or-rotate-a-pdf-prvw11567/mac
(similar to #308)