Decompiling copyrighted third-party software to steal intellectual property, bypass licensing mechanisms (cracking), or create a competing product.
The US Copyright law (17 USC § 117) allows for a "backup copy" or modification of software to maintain functionality. If you own a license to the software (not just a runtime), and you need the source code to fix a critical bug because the vendor no longer exists, you have a strong fair-use argument. If you are decompiling a competitor’s app to steal features, you are going to lose in court. foxpro decompiler
Understanding FoxPro Decompilers: How to Recover and Protect Visual FoxPro Source Code bypass licensing mechanisms (cracking)
Decompilation is not magic. It cannot recover what isn't there. foxpro decompiler