The latest version is downloadable through the Battle.net app, the same app required to play the game on the Bnet. If you still have your CD Key then you can link it to your
Bnet account and get access to the game in the app.
Understand that purchasing Reforged simply gives you access to the HD graphics. If you own a copy of Warcraft 3, regardless of when you purchased it, you're able to play with both Reforged players (those who purchased Reforged) and Classic players (those who only have a copy of the Classic game) at the same time.
Some people, I imagine like yourself, didn't like the changes that were required to keep playing Warcraft 3 on the Bnet, so they refused to update their game to the newer patches. Instead, they continued playing offline or by using services like NetEase.
Fortunately, some of the features that were lost like custom campaigns are finally being added back to the game so you shouldn't be missing out on too much by updating to the latest patch. Unfortunately, there are still bugs and issues that may never get fixed, but the game is still in a playable state.