Hi catachav,
Thank you for posting in the Apple Support Communities. It sounds like you're having some trouble uploading files to third party sites directly from the your downloads folder location without opening them, correct? If so, we would love to help see if we can get the issue resolved for you. Please provide detailed answers to the following questions.
What version of macOS are you currently running?
Have you tried moving the downloaded file to a different location and sharing from there?
What is happening when you try to upload a file from the downloads folder? If you're getting an error, what does the error say?
Cheers!