The ads were discovered by software engineer Rafael Rivera, and tweeted the screenshots. The ads however, are not yet released to the public and stable build of Windows 10 - they appear in selected preview builds of Windows 10.
This isn't the first time Microsoft experimented with ads when they did so in Windows 10's built-in Mail app which they later removed. Microsoft might do the same for WordPad too.
In-app ads aren't new, as mobile apps are dotted with them.
What do you think?