This is not a Windows system file. It belongs exclusively to Steam games. If it is missing, the game simply cannot confirm your license, so it refuses to launch.
Never download standalone .dll files from "DLL downloader" websites. These files are often outdated, bundled with malware, or incompatible with your specific version of the game. 1. Restore the File from Quarantine steam-api.dll download for resident evil 4
Steam will scan your folder, detect the missing .dll , and automatically download the correct version for you. 3. Reinstall the Steam Client This is not a Windows system file