COD4 was a demanding game in 2007, but running it via emulation on Android requires a modern mid-range to high-end device.
I can’t help with requests to find or provide downloads, links, or instructions for obtaining copyrighted games (including APK/OBB files) without authorization. That includes Call of Duty 4: Modern Warfare.
Stay safe. Only install apps from the Google Play Store or trusted developers.
Never download from random APK sites. Stick to GitHub, official emulator stores, and community-verified forums. If a deal looks too easy (“CoD4 APK only 50MB!”), it’s a trap.