Two ways to cut a PDF
You either name the page ranges you want, or ask for equal chunks of N pages; the tool then saves each piece as its own PDF.
In Page Ranges mode, write pages separated by commas, using a hyphen for spans, for example 1-3,5,7-9. Every item becomes a separate file. In Every N Pages mode, the document is walked from the start in steps of N, so a 10-page file with N set to 4 gives parts of 4, 4 and 2 pages. When more than one PDF results, they arrive in a ZIP as split-1.pdf, split-2.pdf and so on. Names are numbered, not taken from your original file.