Can we use GPL3.0 software in our own software?
<p>We're interested in a WordPress plugin available in the WordPress repository licensed with GPL3.0.</p>
<p>We'd like to make some modifications, and then use it for a commercial project.</p>
<p>Is this legal?</p>

<p>Yes, so long as you adhere to the terms of the GPL itself, including releasing any changes you make and any code that the GPL extends to in this case (you will need advisement on this, as it depends on how you are using the GPLed code as to whether it extends to other code in your codebase).</p>
<p><a href="https://www.gnu.org/philosophy/selling.en.html" rel="nofollow noreferrer">https://www.gnu.org/philosophy/selling.en.html</a></p>
<blockquote>
<p>Except for one special situation, the GNU General Public License (GNU GPL) has no requirements about how much you can charge for distributing a copy of free software. You can charge nothing, a penny, a dollar, or a billion dollars. It's up to you, and the marketplace, so don't complain to us if nobody wants to pay a billion dollars for a copy.</p>
<p>The one exception is in the case where binaries are distributed without the corresponding complete source code. Those who do this are required by the GNU GPL to provide source code on subsequent request. Without a limit on the fee for the source code, they would be able set a fee too large for anyone to pay—such as a billion dollars—and thus pretend to release source code while in truth concealing it. So in this case we have to limit the fee for source in order to ensure the user's freedom. In ordinary situations, however, there is no such justification for limiting distribution fees, so we do not limit them.</p>
</blockquote>

gpl