IN INDESIGN, I made an a4 document with a beige rectangular box as a master page and then this was present on all the pages. This document was named as Document A
Then in a new blank document of 12inches x18inches paper size. I imported a4 pages from Document A [in indesign format ], one by one. The document was imported nicely but the beige rectangular box was not imported [that was in the master page]. What is wrong? I am using indesign cs6
Nothing is wrong.
When you move content between documents if they have styles, swatches or master pages that have the same names, the ones in the destination document are used rather than the ones from the source. To bring over a master page when moving pages the name of the master page must be differnt from any master in the document you are moving pages into.