The document would be more fields/Content Controls

Eg


Select an option:
Combo Box option 1
Combo Box option 2
Combo Box option 3
Combo Box option 4


If CBO option 1 is chosen, enter "This block of text"
If CBO option 2 is chosen, enter "This other block of text"
If CBO option 3 is chosen, enter "The third block of text"
etc


Maybe this can be done easily with VBA or a Macro?