That is why most objects have resistance to damage. Adamantine weapons are a special, optional case. Attacking a shield will wear it down, unless the shield is magical. Historically, knights had way more than only one shield. Three or four would be closer to the truth. And while you attack the shield, you don't attack the holder of the shield. The few rounds it will take you to destroy the shield (and good luck if the shield is adamatine) you will be attacked by the holder of the shield. Normally, this is a losing strategy.
As for the scroll in hand.
Attacking it would not be hard, and I would give 3/4 cover as the person holding it will try to prevent it to be destroyed. But attacking a scroll will result, if successful, in its total and immediate destruction. Depending on what is on the scroll, this is a win situation at all times. Of course, a player (or an NPC) might bluff with a blank sheet of parchment, but it would be a risk most would be ready to take as you never know what will be on that scroll.
As for attacking a bow.
Perfectly fine option and dare I say:"Even optimal". If you are in hand to hand with a bow. You did something wrong and should die. It was so in history and should be so in D&D. Drop the bow as 100% of people in history did and pull out your short sword (or rapier) from its scabbard. Ready your buckler and hope that the big fellow with an axe comes to your help.
QUOTE="Stoutstien, post: 8176334, member: 7020569"]
Not possible. Using a scroll still counts as casting the spell so the normal rules for spell per round limitations apply.