The file extension GRD marks gradient files, ie gradient files of the image editing software Adobe Photoshop. Grd files contain color value information and settings such as gradient type (linear, radial). It can also contain entire collections of color gradients.
Gradients can be applied to shapes or image areas and are automatically adapted to the respective size. In order to use a downloaded GRD file, you can set the drop-down menu to color gradients and load GRD files under 'Edit-> Preferences Manager'.
Usually GRD files are stored under 'Preferences / Gradients' in the Photoshop main directory. For example, gradients are automatically displayed when using the Gradient tool.