Is there a web service for converting HTML to PDF?

For third party solutions there are lots of options. Just to name a few...

• https://cloudlayer.io
• https://www.api2pdf.com
• https://www.printfriendly.com
• https://pdfshift.io
• http://pdfmyurl.com/html-to-pdf-api
• https://www.html2pdfrocket.com/
• https://pdflayer.com/
• http://pdfcrowd.com/
• http://www.pdfonline.com/convert-pdf/
• http://docraptor.com
• https://restpack.io/html2pdf
• https://products.aspose.cloud/pdf
• https://pdfmage.org/

You could use the Python ReportLab library from Google's AppEngine, or if you are happy to use a 3rd-party service, PDFCrowd will do this for you.

DocRaptor should do the trick. It's a web service, so you'll be able to give your server a break.