Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
In addition to the suggestions by Palcouk, start the system in clean boot to check if any non-Microsoft application is causing the problem and try downloading the file again.
Note: Read the disclaimer mentioned in the article.
http://support.microsoft.com/kb/310353
Note: Once the trouble shooting is done, start the system back in normal mode.
Ruchi Bisht