"Can more than one document, pdf or excel be present in a container field" - No. If you want that concept, have a portal of container fields with the files in them.
"I have right clicked and inserted a file and the correct pdf icon appears, but it does not open when I click it" - Try 'Store by reference only' then it should open.
If you insert many files (as opposed to 'by reference only') into your file its size will balloon, BTW.
Works a treat - many thanks.