Common Display File (Header + File-level Keywords)

I learning about RPG and DDS for screens and I am trying to determine if there is some method of including or referencing one DDS screen inside of another. What I want to be able to do is create a "common" display file that has, for instance, the company name and the date, and includes some file-level keywords and allowed function keys (INDARA, CA03, etc.). Then, ideally, I would be able to create program-specific screen content in a separate file without having to redefine the common function keys, header information, and file-level keywords.

Is there a method of including DDS source with something like a /copy? Or can I use two display files in one RPG program and have their allowed keys and keywords both active at the same time? I have tried using two in one program, but I can only get them both to display by using EXFMT rather than WRITE for the header file, which means control needs to be returned before the main screen is written. If I use a WRITE header followed by an EXFMT main screen, only the main screen is displayed and none of the file-level keywords from the header are active.

I have also seen advice to designate a header field in your display file and customize it in your program in order to allow a more standardized header, but I don't know how (or if) it can be used with file-level keywords and allowed function keys?

If this is not possible, how is screen standardization usually handled?

Thank you,
Sarah