Keep in mind that all missions do not have Tomes/Grimoires.
While looking at the mission map, missions with a golden border will have the items and the silver border ones will not.

For russian translation go here (Thanks PitFighter )
Thanks to Chaplain Lithius for showing me the Karak Azgaraz and Stromdorf locations

A tome is a book held in your medical supply inventory slot.
Carrying a tome to the end of a level will change one (per Tome, max 3) of your loot dices from a dice with 1/3 chance of success to a 2/3 chance.
Tomes can be dropped to pick up healing supplies to heal and then be picked back up during the mission.
The Tome does not have any other uses or special effects.

A Tome dice



A Tome in-game

A Grimoire is a book held in your potion inventory slot.
Carrying a tome to the end of a level will change one (per Grimoire, max 2) of your loot dices from a dice with 33% chance of success to a 100% chance.
Grimoires cannot be dropped, and if used (discarded) cannot be reclaimed and is lost.
Carrying a Grimoire will lower your entire partys maximum health by 33% per Grimoire.

A Grimoire dice



A Grimoire in-game

Thanks to Rats Chats for this.

Thanks to Rats Chats for this