Fix case-sensitive file ending checks

encrypt.py

@@ -77,7 +77,7 @@ def main(args):
     starttime = time.time()
     pdf_folder = os.listdir(infolder)
     pdf_files = [_ for _ in pdf_folder
-                 if _.endswith(".pdf")]
+                 if _.lower().endswith(".pdf")]
     print("""
 Available PDFs to be encrypted:
 - {}