Article: Tap the Files app icon, which resembles a blue folder on a white background. This will generally open the last section of the Files app that you had open. It's in the bottom-right corner of the screen. This will open the "Browse" page, which lists all of the Files app's folders, including the On My iPad section. Tap On My iPad, then tap the folder in which you saved the video. You should see the video here. For example, if you saved it in the "Pages" folder, you'd tap On My iPad and then tap Pages to view the video file. Tap your downloaded video to open its page. It's in the bottom-left corner of the screen. Doing so will open a menu. This option is at the bottom of the menu. Selecting it will save a copy of the video to your iPad's Photos app, from which point you'll be able to watch the video from there whenever you like. At this point, you can delete the video from the Documents app without the video disappearing from your iPad's Photos app.

What is a summary?
Open your iPhone's Files app . Tap Browse. Open your video's folder. Select the video. Tap the "Share" icon . Tap Save Video.