Use the HDR (High Dynamic Range) merging tool to combine three different exposures of the same scene in order to preserve details in the shadows and highlights. The HDR tool can be found by clicking the HDR icon on the Tools tab of the toolbar.
Clicking the HDR button will open a file browsing dialog. Select the dark, medium, and bright images by holding the Ctrl key and clicking on the files. Once you have these images selected, click Open.
Photopad will now automatically align and combine your images into a single HDR image, which you can continue to edit like any other PhotoPad Project.