C# .NET API to add, search and remove image & text-based watermarks from documents: PDF, Word, Excel, presentations, Visio, email and image file formats....including: PDF, Microsoft Word, Excel, PowerPoint, Visio, OpenDocument...XLSX, XLT, XLSM, XLTX, XLTM PowerPoint: PPT, PPTX, PPS, PPSX, PPSM...