The site has a snippet of code showing high level logic around what impossible combination of file types will give flags. One file that's both a JPG and a JAR. Those calls for check_PDF didn't appear to be from any standard Python library, though I'm not that great at Python. There are a LOT of reference to Erwin Schrodinger except for what he's most known for, his quantum mechanic's thought experiment about a cat in a box. So cat the files together and upload them for each flag portion and you get....
"shkCTF{Schr0diNgeR_" and "_w4s_A_gRea7" and "_p01yg1o7_4e78011325dfbe4a05fd533ea422cc94}"
Flag:shkCTF{Schr0diNgeR_w4s_A_gRea7_p01yg1o7_4e78011325dfbe4a05fd533ea422cc94}