How Split PDF works
Extract, delete or reorder the pages of a PDF with pdf-lib. Open your document, pick exactly the pages you want to keep and the order you want them in, then download the new file.
Select any subset of pages, in any order, and the tool builds a fresh PDF from exactly those pages while the unselected ones are left out. This is the opposite of merging, so you can split out the pieces you need, then recombine them with the PDF merge tool.