If you have already downloaded it, do not double-click it.

The second extension (the one at the very end) is the true file type. In many cases, a file like document.pdf.exe will appear as just document.pdf because Windows and other operating systems often hide "known file extensions" by default.

If this file was sent via an unsolicited email or downloaded from a suspicious site, delete it and empty your trash. Check for and remove duplicate file extensions in same file