It´s possible to include a grid with Joomla?
Sure it is.

What is the way to adapt a grid with Joomla?
Like in any other. If your experienced it should be done within 20 minutes for a module or 1 hour for a component depending on the scope of freedom you want to give the administrator.

Exist any Joomla-component to do it?
Lots of them i assume. i myself use a component including modules and plugins to full extend of jqgrid since my beginning here. though most are not shared yet. if i got time i might create a proper download for it.

For a simplest implementation you just use a module as a wrapper and you have your grid within 2 minutes displayed in any moduleposition within your joomlatemplate.

Your second question:
Jgrid is "only" (not literally 🙂 ) a javascript solution. you have to build the whole serverside part yourself or buy the commercial edition which gets you started immediately.

If you use only static local data, serverside is not needed. Otherwise build the rest yourself searching the forum or just examining the code. there are great people here to help like oleg and tony. You might search for oleg's advise already given at stackoverflow.com, its worth a look trust me.

My second question: I made an example with examples-folder (examples/editing_data/edit_add_delete), and the information appears, but icons "add", "delete" or "modify" it doesn´t work. I dont know if the reason is because I have a free download and is not paid-version. I´ve tried with another examples and I couldn´t make work with add/delete/modify.

Thanks