Pages, not just files
Switch to Pages to see every page of every file in one grid: move a page from one file into the middle of another, turn the sideways ones, drop the blanks.
Combine PDFs into one. Put the files in order, or switch to pages and arrange every page by dragging. Bookmarks, links and form fields come along.
Drag to reorder. With the keyboard: arrows to move between, Alt + arrows to move one, R to turn, Delete to remove.
Switch to Pages to see every page of every file in one grid: move a page from one file into the middle of another, turn the sideways ones, drop the blanks.
Links between pages still work, bookmarks can come along under each file’s name, and form fields stay fillable. Fields with clashing names are kept apart.
Merging happens in this tab, however many files and however large. Password-protected files ask for their password and stay on this device.