Thanks for your interest in GroupDocs.Watermark.
Yes, you can make the watermark read-only and invisible using GroupDocs.Watermark.
To control the visibility of the watermark, GroupDocs.Watermark provides setOpacity method in TextWatermark and ImageWatermark classes. To make the watermark invisible, you can set the opacity to 0 as shown in the following code sample.
CellsDocument doc = Document.load(CellsDocument.class, "document.xlsx");
// Adding text watermark
TextWatermark textWatermark = new TextWatermark("Test watermark", new Font("Arial", 8));
// Adding image watermark
ImageWatermark imageWatermark = new ImageWatermark("watermark.png");
To make the watermark read-only, GroupDocs.Watermark provides the locking mechanism that indicates whether editing of the watermark is forbidden or not. In order to lock the watermark, setLocked method is used which is available in the following classes:
To protect the removal of the watermark from PDF documents, GroupDocs.Watermark provides PDF document rasterization. This feature converts the PDF document’s pages into raster images which makes it almost impossible to remove the watermark. For details on this feature, please visit this documentation article.
In case you would have any other question or query, please feel free to let us know.