Problem with uploading and downloading files [closed]

I made a php on the website, there is an option to import files on the website, when I mention the normal opening of the pdf from my computer, it will buy a cheat site, I open it, look in the backpack, there is a file, I open the database, paste the file name is normal, but when I download from the website the back file writes that it can not save the back pdf file For your experience, the file in the cheat panel worked fine dragged to work properly file name is index.php: all codes in GitHub

https://github.com/vamkrtch/site.git: [1]: https://i.stack.imgur.com/3s4de.png [2]: https://i.stack.imgur.com/GMK9v.png