Approvals can be done for anything - currently there is support for: Business Trips, Borrowing Items, General Approval, Contracts, Payments, Car Rentals, Job Applicant Referrals and Procurements (Purchasing).

You can define your own approval and require any or all of the following information to be required or optionally supplied on the request:  Documents (attachments), Contacts, Dates/Periods, Items, Quantities, Amounts and Locations.

​The Manager of the employee can automatically be added to the request, and you can also define additional approvers and even the number of individuals who have to approve a request.

An Activity is created automatically for the Approver(s) to Approve or Refuse.

The Documents App is tightly integrated right now more with Accounting (OCR of Vendor Bills) but with a small customization can be linked to another other Business Document type that needs more than simple attachments – and this way you can leverage Document tagging, versioning, internal/external sharing, reviews, digital signatures, etc.

https://www.odoo.com/page/approval-workflow

https://www.youtube.com/watch?v=7E8MgurpWKQ

https://www.odoo.com/documentation/user/13.0/discuss/plan_activities.html

https://www.youtube.com/watch?v=WFxdxNx8iKE