Add a button to a form without of changing that form

Good mooorning!

I saw somewhere that there is a possibility to add a command to item or list form without of need to change that form. Have someone tried this? Please explain how can I do that?

See common commands for that. If you specify the command parameter type as, for example, reference to some catalog, this command will appear in command bars of list and item forms for this catalog. Except for case when those command bars are filled manually.

I attach example where I add command, and then add it as button to Form command bar and to context menu of field

Thank you, I've got it!