Use a utility like 7-Zip or WinRAR . Right-click the file and select "Extract to 21787/".
Some hardware manufacturers use numeric IDs for driver packages. Check the website of the hardware you are trying to update. 21787.rar
Generic numeric filenames (like 21787.rar) are frequently used to distribute or adware . Use a utility like 7-Zip or WinRAR
If you expected a document or a video and find an .exe file inside, do not run it . do not run it .