The most reliable way to get code_pre_gfx.ff is through your official game launcher. This ensures you get the exact version required for your current patch. Open the Battle.net client. Select Call of Duty: MW in your library.
If a simple scan fails, you may need to force the launcher to re-examine the files by deleting corrupted metadata: Download Zone Code Pre Gfx.ff Modern Warfare.rar
Click the (cogwheel) icon next to the "Play" button. Select Scan and Repair . The most reliable way to get code_pre_gfx