After loading a PDF, every page is rendered as a thumbnail using pdf.js so you can see what you're extracting before committing to it. From there you can pick individual pages by clicking their thumbnails, type a range like 1-3, 5, 8-10 to pull out one combined PDF, or split the whole document into equal-sized chunks — each chunk becomes its own PDF file, and when the result is more than one file they're bundled into a single ZIP download.
Separate individual pages or ranges with commas — 1-3, 5, 8-10 extracts pages 1 through 3, page 5, and pages 8 through 10, all combined into one output PDF in that order. Page numbers outside the document's actual page count are simply ignored rather than causing an error.
Every chunk gets the number of pages you set except possibly the last one, which just takes whatever pages remain. A 10-page document split into chunks of 4 produces three files: pages 1-4, pages 5-8, and a final file with just pages 9-10.
No — if the PDF is encrypted or password-protected, page rendering will fail and you'll see a message that the file couldn't be read. You'd need to remove the password protection first before splitting it here.