??(f) REVERSE ENGINEERING.?(1) Notwithstanding the provisions
of subsection (a)(1)(A), a person who has lawfully obtained the
right to use a copy of a computer program may circumvent a technological
measure that effectively controls access to a particular portion
of that program for the sole purpose of identifying and analyzing
those elements of the program that are necessary to achieve
interoperability of an independently created computer program with
other programs, and that have not previously been readily available
to the person engaging in the circumvention, to the extent any such
acts of identification and analysis do not constitute infringement
under this title."
That's from section 1201 of the DMCA.  You still need to legally own a copy of the software, but if for reasons of compatibility it doesn't work with other software (can make the argument that your copy of MS Office doesn't work well with your copy of Linux) you should have the right to go in and tinker to make them play nice together.