I had been trying create an application to sign digital signature to Office documents and, optionally convert them to PDF. I tried many different libraries (both free and commercial), but they did not have features that I need (e.g. signing digital signature on Microsoft Signature Line, finding objects in Office documents, etc.). When I found Aspose.Total for .NET, I was able to finish my development within a week. This is a fantastic library for manipulating all kinds of documents.