As is further discussed in Boilerplate text, you can 'assemble' documents by simple calls to other documents. These calls don't involve the document assembly screen, but rather just typing text references to documents located in the Boilerplate folder (or a sub-folder off that parent).
If you want to recall the document using your keyboards, just type the name of the document and then press Alt-G.
If you wish to embed a document into another document so that the text of that document will be automatically inserted in the new document during the assembly process, enclose the document name within two angle bracket sets (greater than and lesser than characters) E.g.,
(Just the base name of the document is needed. Do not add a .doc or .docx extension.)