I'm curious if this is happening for you when you attempt to upload any file or just a pdf? If this happens whenever you try to upload any file there is probably a permissions issue in with the directory specified: D:\Hosting\5457446\html\files\.
Please let us know if you have been able to upload any other files. Also, based on the name of the file in the error message it seems there could be a problem with the file name. What is the specific name of the file you attempted to upload?