Common reasons to split a PDF
Extracting one chapter from a long ebook or report. Pulling out a single invoice from a combined billing PDF. Removing personal pages from a document before sharing the rest. Sending only the signed pages of a contract instead of the whole file. Building a smaller version of a document for email by dropping unnecessary pages.
All of those use cases are solved the same way: identify the page or pages you want, split them out, and discard the rest.