You should never download a standalone .exe file from a random third-party website, as these are often used to distribute malware. If the file is missing or corrupted, the only safe way to "download" it is by using your game launcher to verify and repair the installation:
Stay safe, and happy gaming!
To safely download and play GTA 5 using the GTA 5.exe file: Play Gta 5.exe File Download
(Link to official store) [Buy GTA V on Steam →] (Link to Steam store) You should never download a standalone