Azzanadra's seal is lost when you "find it on the ground and RuneScape gold pick it up by itself". That means that in the event you're not able to locate Azzanadra's seal or other similar items, and using the prayer to protect items that those items as well as the seal will remain yours.
When you invoke the seals, they'll give you a unique effect. Imp Invoking grants you the Rusty Imp Dagger. This will give you -10 strength, but no other stats. If you are attacking an opponent that is easily pickedpocketable the damage you cause will be determined by the number of times you steal from them without being arrested. If you attempt to attack an opponent whose ability to steal is not enough it will be a fight only the enemy.
The secret +5 bonus to theft is provided by the dagger. If you take on an opponent with the dagger, and then commit 35 theft occurs, you can take their money. The seal will be destroyed after you've obtained the item and defeated Zamorak. If Azzanadra's Seal is in your inventory, an imp could grant you a new seal in the event that the dagger is lost.
You'll get black sword shreds when you invoke the lesser Demon. More Demon activating will give you red sword chunks. K'ril Tutsaroth: Invoking it will give you demonic blade designs and the sword's hilt. The Demon Butler (it is known by the item name that is Alathazdrar's Seal, but the information on its examine states it's the demon Butler's) Invoking it will send you to Sergeant Damien. If you invoke it again, it will grant you 200 curry bowls.
Sergeant Damien's prayer will grant you camo gloves and boots, as well as dog-tags. These aren't random events, therefore they can't be put in the closet. Once you have all the pieces and plans you've gathered from your seals, you can use them to create the Demonic Blade. You can create the demonic sword making use of buy OSRS gold one of the parts of the anvil.