Removed app is still available - how to remove it? I just removed Calibre app via Finder Cmd+Backspace. The app cannot be found via F4 key now. But it is still available via context menu "open with", even two versions there. So how app can be really removed?

macos 10.12.6
If you are trashing an app manually, then you have to delete it's supporting files. Those could be in Application Support, Contextual Menu Items, Preferences, Receipts etc folders.

Use apps like AppZapper to uninstall apps completely with all the related files. It's a paid app, but it works very well.