Send an email to responsible(s) in accordance with item selected in the "definied" field

HELITON CHIARETTO‌ I think you have to provide here some more details. I will try to break-down your description and then you tell me if it helps. For the start - I would suggest to use a "state machine" (and a boolean variable telling if any changes to the request must be made) so that you would be able to go back to the requester as long, as you want

1. Send an email to responsible(s) in accordance with item selected in the "definied" field.

What I understands is that you have some sort of a form where user can choose value. Then based on the value that is chosen a different approver/ responsible person is taken. 

If I'm correct then what I suggest here is to assign the person e-mail to a variable, let's say - CurrentApprover. Then workflow moves to a state dedicated for the Requestor where actions can be put like "Send email" confirming Requestor, that his request is in progress.

2. This person when receive this email, will approve or reject the form.

Now I guess as you have the current approver selected you use an action "Assign a task" with two outcomes - Approve or Reject. The action sends an e-mail to the selected approver. You can as well mark the "Lazy Approval" option so the user is able to approve or dissapprove using "Reply to this e-mail" option and writing a proper response (more hrere: LazyApproval in SharePoint Online (Office 365))

3. If form is approved: workflow run the function Document Generation to create and edit a document in Word (*.docx) with the fields filled in the form (Using a predefined template).

When user approves a task then workflow moves to the "Approved" branch where you should place "Document Generation" action and configure it properly.

4. If form is rejected: The form must return to the requester to be corrected.

Now you need to go back to the "Requestor State" but with a different actions in a "Conditional Branch" action (based on the value of the boolean variable) and then waits for the form to be updated.

I see the workflow like the one below:

I really hope it helps you 

If not - post a reply!

Regards,

Tomasz