Reorder, rotate and delete in one pass
These three edits usually arrive together. A scanned batch comes out with pages in the wrong order, some fed in sideways, and a few blank separator sheets that should not be there. Doing them as three separate operations means three uploads, downloads and rounds of checking.
Working from page thumbnails means you are looking at the document rather than reasoning about page numbers — which is where mistakes come from when the numbering in the file does not match the numbering printed on the page.
What happens to the file
The output is rebuilt by copying the page objects you kept, in the order you put them, with the rotation you set recorded in the page dictionary. No content is re-rendered: text stays selectable, images keep their resolution, and vector artwork stays vector. Deleting a page removes it from the copy only — your original is never touched.
To combine several documents, use Merge PDF; to break one apart, Split PDF. For a document that is simply too large, see Compress PDF.