Can I use 现代汉语词典 outside of the paper dictionary? 现代汉语词典 seems to be the de facto standard for Chinese dictionaries. Some users here use it as well. But it seems only possible for the paper version.

But I might miss something. Is it possible to use it outside of its paper version, such as online or app? I searched for it on the App Store, but seems that there are too many results and I don't know which is the correct one (actually all of them don't seem to be official ones...). Also I really hate it if I purchase an app but later found some words are missing.

Or is it only available on the paper-version?
You can buy it as an in-app purchase in the Pleco app. It costs 19.99 USD at the moment. For Android devices and also for iPhone /iPad. Reference: http://www.pleco.com/products/pleco-for-iphone-ipad/pricing-bundles/ in the section "Individual Add-ons /dictionaries ". If you install Pleco for free with just the 现代汉语词典 as an extra it should just cost 19.99 USD.