wow that looks really nice.
actually we mostly do html to pdf, but maybe I can look into your project and try to add it (if there is a nice html/dom library like java has with jsoup).
basically we don't need a lot, mostly switch fonts/text sizes/images (generated barcodes, logos) and of course pdf/a-3(a/b/u) for invoice. so apis that translate the html into the layouting of pdf is the bigger problem.
Yeah HTML to PDF is a tricky one, presumably wkhtmltopdf/pechkin doesn't work out because of licensing / interop issues? Other than that the only other one I'm aware of is Aspose which is expensive as you say.
Images (along with font subsetting and fixing the gzip implementation) are the next thing I plan to implement so it's helpful to know its a real requirement.
actually wkhtmltopdf/pechkin both won't support pdf/a-3 and have a not so nice output.
aspose is actually really cheap, compared to others, unfortunatly their support is trash: https://forum.aspose.com/t/html-to-pdf-pdf-net-fonts-error-o... i.e. pdf/a-3 does not work on mac (didn't tried linux, but I guess it has similar problems)
btw. itext is a really great library, unfortunatly itext has a problematic licensing and I tought they were jocking after they gave me prices.
basically we don't need a lot, mostly switch fonts/text sizes/images (generated barcodes, logos) and of course pdf/a-3(a/b/u) for invoice. so apis that translate the html into the layouting of pdf is the bigger problem.