I build such a service, but it is impossible to guarantee any reliable result. I ended up shutting it down.

The PDF standard is a mess, and the number of 'tricks' I've seen done is astonishing.

Example: to add shade or border effect to text, most PDF generators simple add the text twice with a subtle offset and different colors. Result: your SaaS service returns every sentence twice.

Off course there were workarounds, but at some point it became unmaintanable.