Please note: this procedure works on all Windows 10 Lumias, even the x50 (like 550/950) if your Windows 10 is at version 1703 or lower.

How to check your Lumia's Windows version
How to downgrade your Lumia's Windows version to 1703 or lower

  1. install 8zip on your Lumia
  2. download from the Lumia itself
  3. touch the downloaded file and 8zip will open it, then long-tap the Internal Memory.lnk file and select Extract to Documents folder
  4. tap the extracted Internal Memory.lnk and an unrestricted file manager will open, letting you access the unencrypted messages.db!

You'll find the messages.db at one of these locations:



Phone\Data\USERS\DefApps.Windows Phone\APPDATA\Local\Packages\5319275A.WhatsApp_cv1g1gvanyjgm\LocalState\messages.db

If the 1703 procedure does not work for you, even if requirements are met, as a last resort you can try the Interop procedure.