"Split this PDF" can mean three different things depending on what you actually need afterward, and picking the wrong method just means doing the job twice.
Splitting by page range
Use this when you know exactly which pages belong together — for example, pulling pages 5 through 12 out of a 40-page report to send as a standalone excerpt. You specify the range once, and get a single new file containing just those pages.
Splitting into equal chunks
Useful for breaking a long document into evenly sized parts — a 100-page manual into ten 10-page sections, for instance. This is the right choice when the split point doesn't need to align with the document's actual content structure.
Splitting into one file per page
The most granular option, producing a separate PDF for every single page. This is typically what you want when each page is actually a distinct document that happened to get scanned together — multiple invoices scanned in one batch, for example.
What happens to page numbering
Split files retain whatever was originally printed on the page as an image or text — if page 15 said "Page 15" in the footer, that doesn't renumber to "Page 1" just because it's now the first page of a new file. Plan for that if the split files are going to a reader who'll notice the mismatch.