This is the 11708th most frequent Russian word.
заверена
Certified.
Here, 'заверена' is used in the past passive voice to indicate that the document has undergone the action of certification by an official source.
Документ был заверен у нотариуса.
The document was certified by a notary.
In this sentence, 'заверена' is used in the passive voice future obligation context, suggesting it is necessary for the document to be authenticated.
Копия заявления должна быть заверена.
A copy of the application must be certified.
This usage of 'заверена' refers to the letter being validated or authenticated through the placing of a seal.