Three ways to cut, and when each is right
By range is the one you will use most. You name the pieces you want — 1-3, 7, 12- — and get one file per piece. It is how you pull the signature page out of a lease, or separate a bank statement into months. Ranges may overlap, and they may run backwards: 9-5 gives you those five pages in reverse order, which is occasionally exactly what a badly scanned document needs.
Every N pages cuts a long document into equal chunks. It is the right tool for a portal that will not accept anything over twenty pages, or for splitting a book into chapters of fixed length.
One file per page does what it says, and names the files with zero-padded numbers so they sort correctly in every file manager — page-01 through page-09 rather than page-1 through page-9, which sorts 1, 10, 11, 2.
How to write a range
Commas separate files. A hyphen makes a run. Leaving one side of the hyphen empty means "to the end" or "from the beginning", so 12- is page twelve onwards and -4 is the first four pages. A single number is a single page. Every range you type becomes its own PDF, named after the range it came from, which is what makes the ZIP readable when you open it a week later.
Splitting does not degrade anything
Like merging, splitting copies page objects rather than re-encoding them. Every extracted page keeps its text layer, its embedded fonts and its images at full resolution. A page pulled out of a document is byte-for-byte as good as it was inside it — the only thing that changes is that unused fonts and images from the pages you did not keep are left behind, which is why the pieces usually add up to less than the whole.
The ZIP is built here too
When a split produces several files they are packed into a ZIP inside this tab, by a small archiver written for this site rather than a third-party library. Nothing is uploaded to make the archive, and the result is an ordinary ZIP that opens in Windows Explorer, macOS Archive Utility, or any command line. It is stored rather than deflated, because PDFs are already compressed and squeezing them again would buy a percent or two for a lot of work.
If you only want a couple of pages rather than a set of files, use Organise pages instead: select the pages you want, choose "keep only", and download a single document.