The batch-scan problem this solves
This usually comes up after a scanning session, not before one: someone fed twenty invoices through a scanner and it spat out a single 20-page PDF, but your accounting software or filing system wants each invoice as its own file. Doing this by hand means opening a PDF editor, deleting everything except one page, saving, undoing, and repeating twenty times — a genuinely miserable way to spend an afternoon.
A split tool flips that into one action: upload the 20-page file once, and get back twenty separate one-page PDFs, already named in order. What used to be a repetitive half-hour chore becomes a single upload.
Why it comes back as a ZIP, not twenty downloads
Browsers don't handle a page trying to trigger twenty simultaneous downloads gracefully — some get blocked as pop-ups, others land in a random order in your downloads folder. Bundling every split page into one ZIP file sidesteps that entirely: one download, then you extract it once and get all the files together, already sequentially named (page-1.pdf, page-2.pdf, and so on).
That sequential naming matters more than it sounds like it should. If invoice #7 turns out to be the one with a mismatched total, you know exactly which file to open without checking each one.
Splitting vs. extracting — pick the right tool
It's easy to reach for split when you actually want extract, or the other way around. Split is for when you want every single page as its own file — you're dividing the whole document. Extract is for when you want a handful of specific pages pulled together into one new document — say, pages 4 through 7 of a 40-page report.
A useful rule of thumb: if you'd end up wanting most of the resulting files back merged into a smaller group anyway, you probably wanted extract, not split.
One-page PDFs and other edge cases
A single-page PDF has nothing to split, so the split action is disabled for those — you'd just get an identical copy back, which isn't useful. It's a small guard rail, but it saves you from a pointless download.
Encrypted PDFs are the other common snag: a password-protected file needs its password removed before any page-level operation can read its contents. Run it through a PDF unlock tool first, then split the unlocked result — trying to split the still-locked file will just fail to load.