Overton tracks more than a thousand different sources of policy documents in 90+ different countries. New documents from those sources are automatically added to the database.
If you're logged in to Overton then you can see a complete list of sources on the Sources page. Users can request adding a specific source by emailing support.
There isn't a broadly accepted definition of what a "policy document" is. Overton defines them very broadly as documents written for or by policymakers.
We collect policy documents from governments and official bodies but also from IGOs, think tanks and some NGOs: groups whose output is often aimed at influencing policy.