Any graphics file or document can be simply printed to PDF format with any tool that can view and print the content. In case of RS format, which is a raster format, this should be doable with any graphics viewer that can open .rs files, for example XnView.
Of course several different types of .rs files exist, so perhaps more than one of such exports is actually possible. In any case you will still need a tool that can open and print your .rs file in order to make rs to pdf conversion.
Updated: October 17, 2023