Last year I wrote a couple of similar "local" PDF tools that run in the browser with no network requests. Each is just a single HTML file that will work offline:

- https://shreevatsa.net/pdf-pages/ is for extracting pages, inserting blank pages, duplicating or reversing pages, etc.

- https://shreevatsa.net/pdf-unspread/ is for splitting a PDF's "wide" pages (consisting of two-page spreads) in the middle.

- https://shreevatsa.net/mobius-print/ is the earliest of these, and written for a niche use-case: "Möbius printing" of pages, which is printing out an article/paper two-sided in a really interesting order. (I've tried it and love it.)

These don't use WebAssembly, but just use the excellent "pdf-lib" JS library. To keep the file self-contained, I put the whole minified source into a <script> tag at the bottom of the (otherwise hand-written) HTML file.