PDFLiner is the all-in-one online platform for working with PDF documents. Here, you can upload any PDF or Image and edit it in just a few seconds. With PDFLiner you edit your PDF files as well as sign them electronically and protect them with password and watermark if needed. It also has an extensive fillable Forms Library with many useful forms. You can just find the one you need and fill it out. It is not open-source.