I'm itself hard to answer to this question. In means of "minimal valid raster image" - its raster image with 1px × 1px; in means of "minimal valid vector image

I'm itself hard to answer to this question. In means of "minimal valid raster image" - its raster image with 1px × 1px; in means of "minimal valid vector image" - its vector image with single dot OR single line segment. But I can't imagine what is "minimal valid raster PDF" means.