No, when you send, it must be from an address that you've previously received money at. At a technical level, this is simply how Bitcoin works: not account/wallet balances, but transactions to/from addresses.
The way that Armory sends and receives bitcoins is fairly privacy-conscious, but you should still assume that someone determined could figure out which transactions are yours. If you want to obscure this to a high degree, use a bitcoin mixer of some kind or CoinJoin.
When I send from my wallet it shows where it comes from, showing all my founds in it.
The public transaction will only show the addresses involved in the transaction, which will typically not be *all* of the addresses in your wallet.