When hunting for IPA files on the internet, be careful. Only download from reputable sources or create your own backups. Unsigned IPA files from sketchy websites can contain malware, though this is less common for older 32-bit apps.
Not every old IPA will work. Here is a real-world compatibility list based on community testing. ipa files for ios 712
Under the DMCA (USA) and EUCD (Europe), circumventing DRM (FairPlay encryption) is illegal. However, if you own a legitimate copy of an app and extract the IPA from your own device or iTunes backup, you are generally on safe ground for personal use. When hunting for IPA files on the internet, be careful