When I "Copy To Device" the file format is not supported

So I take the pictures which I want to take and then "Save as PDF" and then those files get uploaded to Document Cloud and when I "Copy To Device" I can't open the file because I get unsupported file format error but the extension does say .pdf

But if I upload this file to my Google Drive and download it back again the same file is detected as a normal PDF and I can open it. Please fix this problem.