DocuSign - Try DocuSign's interactive signing demo now! Send yourself an electronic document to digitally sign using our e-signature service.
pdflayer - Free, powerful HTML to PDF API supporting both URL and raw HTML conversion. Unlimited document size, lightning-fast and compatible PHP, Python, Ruby, etc.
RightSignature - Contracts, NDAs, forms, you name it — all signed online in minutes
PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
airSlate SignNow - Electronic signature that scales with your workflow
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents