Several open-source alternatives already exist. All are powered by pdf-lib, with the first two also utilizing PyMuPDF.
- BentoPDF (12.3k stars): https://github.com/alam00000/bentopdf
- PDFCraft (3.6k stars): https://github.com/PDFCraftTool/pdfcraft
- PDFLince (31 stars): https://github.com/GSiesto/pdflince
Since this project likely uses the same stack, I’m not sure what the selling point of a more limiting product is.