Steam will scan your folder, notice the missing text file, and redownload it instantly. 2. Create the File Manually
And remember:
Since 2018, Steam has added official ways to achieve what steam_appid.txt once did. Instead of fiddling with text files: Steam-appid.txt Download Borderlands 2
While Borderlands 2 is available on the Epic Games Store, many players prefer to use Steam's overlay and friend list features. Sometimes, adding a non-Steam game to your Steam library and forcing it to use Steam features requires a manual steam_appid.txt file to bridge the gap between the Epic launcher and Steam's API. Steam will scan your folder, notice the missing
Steam itself will generate this file under specific conditions. If you have ever launched Borderlands 2 directly from the .exe at least once, the file may already exist. Instead of fiddling with text files: While Borderlands
If you can create the file manually in 10 seconds, never download it. A .txt file containing 49520 is not intellectual property; it is a configuration string. Any website charging or requiring registration for this file is scamming you.