Under EU law it is illegal to forbid someone to convert a binary back into source code.
Even further, if I buy a software, and it does not run on my system, I can turn it back into source, modify it, recompile it, and use it as much as I want.
If the original company tries to prevent me from doing this, they commit a crime that can be punished with multiple months of jail for their CEO or 10% of their profit as long as they have that practice.
This isn't entirely accurate. There are restrictions on the legality of decompilation in Europe. The main one being that "...decompilation must be necessary to achieve interoperability with the target program or other programs. Interoperability information should therefore not be readily available, such as through manuals or API documentation."
So, decompilation in order to check for security vulnerabilities or to modify the function of the software for non-interoperability reasons do not appear to be covered.
> if I buy a software, and it does not run on my system,
This would be one example case. As I posted in my comment.
Integration can also just mean for future possible integration – for example, if someone writes a tool that can read a file format, I may decompile it to implement a tool to read the same file format.
Even further, if I buy a software, and it does not run on my system, I can turn it back into source, modify it, recompile it, and use it as much as I want.
If the original company tries to prevent me from doing this, they commit a crime that can be punished with multiple months of jail for their CEO or 10% of their profit as long as they have that practice.