If you need to overlap a watermark to your layouts, it wouldn’t be possible to place it in the master layout, instead, use the Figure tool (toolbox>more>Figure).
The figure tool allows you to resize in any direction an image file.
In this case, I have edited the Cadimage logo in a photo editing program (most image editors would handle transparencies).
In the program I completely edited the logo image to have a transparent background and the actual logo to be 50% transparent and saved as a PNG image with the alpha channel enabled
When the image is placed in the layout overlapping the drawings using the Figure tool, make sure to enable the transparencies.
If the layout is printed, the logo appears like a watermark 50% transparent, this transparency quality will depend of the format saved or published the file, a printed version will likely display the transparency much more accurate than a pdf file.
