GroupDocs.Watermark API allows you to search the possible watermarks placed in any document. You can also search the watermarks that are added using some third-party tool. The found possible watermarks can be removed or their properties can be changed. For more details please refer to the following guides:
Searching watermarks...Editor Product Solution GroupDocs...
Check this guide and learn how to manage document security for PDF, Word, Excel, PowerPoint file types - add password, update password, remove password using GroupDocs.Merger for .NET....Editor Product Solution GroupDocs...