GroupDocs.Signature for .NET is an API that helps you build applications that can sign digital business documents, spreadsheets, presentations, images and PDF files. You can use several types of signature including text, image, barcode and QR-code to digitally secure your files. The digital signature API, allows you to fetch all registered certificates and it gives you advanced search options to quickly locate your required signatures. It also includes an option to customize signature properties, such as, dimensions, shadow, alignment and more.