You can easily use AdGuard with AdGuard VPN. But in case if you are using some third-party VPN — there can be problems.
The thing is, normally AdGuard ad blocker requires launching a local VPN on your device to do its job properly. On Android it’s impossible to run two VPNs at the same time, so you can see where this is going. But luckily there are some ways to circumvent this limitation. If your device is rooted you can switch AdGuard to a “Local HTTP proxy” filtering mode, in fact we even encourage you to do that. This way your device’s VPN “slot” can be occupied by a different app. Additionally, some VPNs allow the use of an upstream proxy (e.g., PIA VPN, Nord VPN) — check if your VPN provider of choice offers this option.
When it comes to our own AdGuard VPN, you don’t need to perform any additional manipulations. We have already set up the integration with AdGuard ad blocker that will be activated automatically once both apps are up and running.