Can I take the source code of the program under the GNU GPL license, modify it and use it for commercial purposes?

Question

Copyright

Is it necessary to keep the source code open?

Answer 1

IANAL, TINLA.
> Can I get the source code of the program under the GNU GPL
Yes , why not? If there is, of course. Well, or if someone promised it to you.
> modify
Yes , of course.
All GNU licenses, including the GNU GPL, are free licenses, and all free licenses return to you the right to make changes by definition. [0]
> and use it for commercial purposes?
D a.
All free licenses return this right to you by the same definition.
> Is it necessary to keep the source code open?
No or yes, depending on what you really want to know.
There is no such clear concept of “leaving the source code open”, and practice shows that under such expressions there can be at least three completely different things. Guessing mercilessly. Explain - you can answer.
[0] https://www.gnu.org/philosophy/free-sw.en.html

Answer 2

possible options