PDF Clown - PDF Clown is an open-source general-purpose library for manipulating PDF documents through multiple abstraction layers, rigorously adhering to PDF 1.7 Specification
Lumin PDF for G Suite - Open, edit and share PDF and Office files in your browser.
PdfPig - Read and extract text and other content from PDFs in C# (port of PDFBox)
DocuSign - Try DocuSign's interactive signing demo now! Send yourself an electronic document to digitally sign using our e-signature service.
PDFSharp - Office & Productivity and Development
GTasks for G Suite - Lets you to manage your Google Tasks from Docs allowing you to tackle your to-do list.