oop - How to create friend structure in c++ builder

Question

I am working with third party dll and using it's methods. As their funcs are not in TForm namespace I cannot use my structure written in my unit before class TfMain : public TForm {} definition.

tried

friend struct SVisDoc{
..
..
} doc; 

Somehow I need to make it friend to be able to use from

void MethName(args) // not in TForm::
{
//I need to use it here
} 

Looked at How do you mark a struct template as friend? but during initialization shows an error.

How can I make my struct friend??