This is the 5174th most frequent Turkish word.
imzaladı
"Imzaladı" means "he/she/it signed."
Here, 'imzaladı' is used in the simple past tense to indicate an action of signing documents that took place in the past.
Ahmet bu önemli belgeleri dün imzaladı.
Ahmet signed these important documents yesterday.
In this sentence, 'imzaladı' again indicates the action of signing, this time specifically the page of a book.
Yeni kitabının son sayfasını imzaladı.
He signed the last page of his new book.
Here, 'imzaladı' is part of a dependent clause and points out the completion of the signing action as a prerequisite for another event.