Any ppt file downloaded from internet is usually remained blocked and hence Presentation cannot be opened

Method One

If you've found that any ppt(x) file does not open after being downloaded, it's likely that MS Office has blocked the file for security reasons.
You must unblock the file to open it:

Method Two

You might want to open the ppt(x) file directly from the download dialog box, in this case you have to allow your MS Office to be able to open any ppt(x) file without blocking it. To do so :