Call to a method in other class

hi,
I tried to call a method in my document class- I wrote my Documant class.Method.
but i got the error - “call to a possibly undefined method through a reference with static type class.” i saw in the forum that my method in the document class should be static, but then i got the error - “udefined property _myBtn” - _myBtn is an object of my btn class that from there i call to a method in my document class…
Thanks in advance!