If you'd rather do it for free weasyprint[2] is the best open source alternative.
Another more affordable option you might want to consider is Urlbox[3]. (Disclosure: I work on this)
Urlbox's rendering engine is based on Chrome. It's been refined over the last 11 years to render pages as images or PDFs[4] that look great. I was a customer for 5 years before I joined the team. Everything we'd tried before Urlbox was a disappointment.
Urlbox probably can't match the power of either Onedoc or DocRaptor, but pricing starts at less than $0.01 per document and drops significantly with scale. If your PDF looks great when saving as PDF in Chrome it should look identically brilliant with Urlbox.
[1]: https://docraptor.com [2]: https://weasyprint.org [3]: https://urlbox.com [4]: https://urlbox.com/html-to-pdf
Edits and corrections on generated PDFs is not provided as the PDFs are signed as-is, however you can attach the metadata to the PDF and rerender with the modifications.
Their PDF conversion is pretty good (I use it for PPT/Word -> PDF conversion), though your product is obviously different and has different/better capabilities for programmatic PDF creation. Still, a reference point.
Pricing page: https://www.convertapi.com/prices
Do not misunderstand. A Stripe for generating PDFs can be great, but for a small team, $0.50/PDF is way more than I can afford (after all, you can create a small number of PDFs without too much fuss). Maybe you are oriented towards large companies?
But isn't that 100x what they're actually charging--at least for an enterprise account? Their pricing page says "from $0.005/doc." (Though I'm not sure how much work "from" is doing there.) Pro tier is, admittedly, more like $0.12 per document (assuming you use your full quota). But still much less than $0.50/
I'm generally very confused by the various assertions in this thread about their pricing. What am I missing?
You can choose which API to use: Headless Chrome, Wkhtmltopdf, Libreoffice, etc.