Support for large PDFs

[oxguy3]

I'd like to use CropTool to extract individual images from very large PDFs, such as The Kentuckian 1956.pdf. However, CropTool seems to hang on these large files, or at least, takes longer to load than I care to wait.

I'm assuming that CropTool is taking forever because it's downloading the entire PDF, but that seems unnecessary. Given that Wikimedia's thumbnail server is able to render full-resolution JPGs of individual pages of large PDFs (e.g. here's page 1 of that yearbook), it seems like CropTool could just download these lightweight JPGs instead of the full PDF.