Your file is processed entirely in your browser and never uploaded: the PDF is read into memory on your own device, the pages named by your ranges are copied into new documents, and each range is offered back as its own download. Nothing is sent to a server at any stage — the tool has no server side and works offline once the page has loaded. Like the other structural tools in this category, splitting copies pages as objects rather than re-rendering them, so extracted pages keep their text layer, vectors, page size and rotation exactly.
Ranges are written the way people say them: single pages and hyphenated spans, separated by commas — “1-3, 7” means pages 1 to 3 in one file and page 7 alone in a second. The count for any span is b − a + 1, because both endpoints are included: 1-3 is 3 pages, not 2. Ranges may repeat or overlap (nothing stops you extracting page 5 into two different outputs) and they need not cover the whole document — pages named in no range are simply left out of every output, which is also how this tool doubles as a page extractor.
Splitting is the natural partner of merging. Split a document into sections, reorder or discard pieces, then use Merge PDF to assemble exactly the document you want; or split a long report into chapter files for separate sharing. What splitting does not do is divide one page into pieces — a page is the smallest unit a PDF has — and it does not shrink anything: the outputs together hold copies of the named pages, and their combined size is usually close to the original's.