I edit Family Tree Notebooks pages using my iPad. In fact, the whole FTN system was created because I wanted to be able to have something I could take with me (via my iPad) when I went out to research.
To use Family Tree Notebooks pages, you need to have a PDF editor. You can use any PDF editing program you're comfortable with, but I use Goodnotes. Goodnotes is a notebook app that lets you add pages to build digital notebooks. The app comes with basic pages loaded (lined paper, graph paper, etc.) but you can use your own pages as well.
I have a tutorial on importing FTN pages as templates. Once the pages are imported, it's easy to add text and images. You can decide whether you want to type to add text or handwrite using an Apple pencil. Personally, I use my Apple pencil so all of the pages are filled out in my handwriting, but I admit that when my hands hurt it can be a bit of a challenge.
If you're going to use your iPad to fill out Family Tree Notebooks pages, don't forget to back up your work. You can either back up manually by sharing/printing the pages once you're done with them or you can back up to cloud storage, which saves a copy of your work on the Internet. Most apps have backup options in the settings menu so don't forget to look!