After opening your PDF file in the program, please click the "Edit" > "Watermark" > "Add Watermark" button.
In the "Add Watermark" window, you can input the text as the watermark and choose the font, size, color, and position.
You can add an image as the watermark from your computer via clicking the "File” and select an image from your computer. If you choose another file as the watermark, you can set the "Absolute scale" of the watermark. In this way, the watermark size will not change no matter what is the size of your PDF page.
PDFelement supports adding the same watermark into multiple PDF documents at the same time. Also, it supports removing watermarks from PDFs in batches.