GroupDocs.Watermar API supports adding the following image file types as image Watermark:
Bmp; Png; Gif; Jpeg. Add image Watermark from local file Following code snippet shows how to add ImageWatermark to a document. If the document consists of multiple parts (pages, worksheets, slides, frames etc), the Watermark will be added to all of them.
advanced_usage.adding_image_Watermarks.AddImageWatermark
// Specify an absolute or relative path to your document. Ex: "C:\\Docs\\presentation.pptx" Watermarker Watermarker = new Watermarker("presentation....Watermark Product Solution GroupDocs...GroupDocs.Watermark Product Family / GroupDocs.Watermark for Java...