It depends on what type of decompressing you want to apply on the PDF file, If the page is a bitmap* you can flatten it to a single image by saving to TIFF, PNG etc. or opening the PDF file in Photoshop.
If the page is PNG or JPG you can load it to a .jpg or .png file format (which you'd then need to convert later), and apply a JPG/PNG layer to the TIFF or PNG as appropriate.