I'm not totally sure what you want to say, but the book has (afaik) no purpose regarding the distribution of the runes.
This is the way it should work:
1) Your adventurer gathers enough ingredients to produce a rune.
2) You send your adventurer into a city with the required buildings for rune inscription.
3) The event should pop up where you are informed that a rune has been produces. (This one: )
4) Now, the text of the event states that the rune is only for the character type assassins ("Für: Attentäter"). You have to decide, which one of your assassins you want the rune to help. Then you have to select this assassin (before selecting any other assassins [probably even characters, I'm not really familiar with how the script works]).
5) Your assassin should now posess the rune.
To sum it up: When the event appears, you have to select the character, you want to give the rune to. If you select any other character (e.g. books, because they are technically characters), this one will get the rune (like the book did in your first screenshot).