Creating a pdf that imports other pdf every time its opened

Basically our corporation has several documents (pdf) that undergo changes from time to time. Openning these separately is fine but most of the time they need to be opened in sets that vary depending on use.
Example:
 
Main Documents 1,2,3,4,5,6
Sets of Documents A,B,C where A = 1,3,5
B = 2,4,6
C = 1,2,3,4,5,6
 
All can be opened independently but when you open Doc A it sources documents 1,3,5 and opens them in a single pdf document. This way when documents 1-6 need to be edited the sets do not need be recompiled.
 
Thanks,
Adam