Hi all,
I managed to find a solution to my problem. See the steps bellow.
In my sharepoint I created two new columns. The Effective_Date is the date of the last review, and the Expiry_Days is the number of days that the document expire.

Here's my flow:
1. Every day at 18h, the flow runs.

2. Get files from the document library.

3. For each value, apply condition 1.
Because I have folders, I have to check it it's a folder or file, because the columns in folders have null values and I get errors.
Condition:
@equals(items('Apply_to_each')?['{IsFolder}'], False)If yes (file) - continue.
If no (folder) - does nothing.

4. In condition 2, I check if the Effective_date <= Today - Expiry_Days, meaning that the document is expired.
Condition:
@lessOrEquals(string(items('Apply_to_each')?['Effective_Date']), string(formatDateTime(getPastTime(int(items('Apply_to_each')?['Expiry_Days']), 'Day'), 'yyyy-MM-dd')))If yes: send email.
If no: does nothing.

I used this site to understand all the functions used in the conditions.
https://docs.microsoft.com/en-us/azure/logic-apps/workflow-definition-language-functions-reference#string-functions
It took me several days, but I'm glad I got it.
Hope this help someone.
Thanks for all the help.