Watermark Eraser works very similar to some of the AI image generation tools or features in the Photoshop Beta -- specifically, after selecting the general, overall area, it will replace everything in that area with an AI generated image that blends into everything else in the image. In a way it's similar to the results you get using an object removal tool like Inpaint, but unlike that sort of tool, the results can be original, not copied or cloned from anything preexisting in the photo. And since it does take preexisting elements in the photo into account, the selection you start with does not have to be exact, but rather just cover the general area. One of the neat things about this is you can just as easily extend a photo, changing the overall aspect of an image, e.g., transforming a narrow shot taken with a phone to 4:3. While Watermark Eraser does have some image editing features, resizing the canvas is sadly not included, so to do that sort of resizing you have to first enlarge the canvas in a photo editing app, save it, then open that new image in Watermark Eraser. Then you simply select the blank portions of the photo and have Watermark Eraser do its thing. It's more work than doing the same thing in the Photoshop Beta, and in a very quick test the results are not as good, but checking the Adobe site this morning they want $20/month.
Getting the GOTD download link via email, I found that this is one of those giveaways where you need to keep the download site open in the browser, copy pasting the URL to get a key before closing the browser. The app by default will install into the Users folder -- you can change that to the more traditional Program Files (x86) if you want. The installed app takes up 244MB with 156 files, 12 folders in the program's folder, + two folders taking up 24MB in Users\ [UserName]\ AppData\ Roaming\. The registry gets an uninstall key, one for the path to the program's files, and one for the app itself.