The file is being stored with a name like "%D0%9C%D0%B0%D0%B3%D0%B8%D1%81%D1%82%D1%80%D0%B0%D1%82%D1%83%D1%80%D0%B0%20%D0%A0%D0%BE%D1%81%D1%81%D0%B8%D1%8F%20%D0%B8%20%D1%81%D1%82%D1%80%D0%B0%D0%BD%D1%8B%20%D0%A6%D0%B5%D0%BD%D1%82%D1%80.%D0%B8%20%D0%92%D0%BE%D1%81%D1%82.%D0%95%D0%B2%D1%80%D0%BE%D0%BF%D1%8B.pdf", which is too long for the file system to handle (most filesystems handle 255 characters).
The way files are stored will not be changed soon, so the most simple solution would be to shorten the filename.
works fine in v4.2