It’s a well-kept secret that copy, cut and paste are supported on iPad and iPhone. It can be a bit fiddly sometimes, but often it’s invaluable. Here’s a video from Apple that shows how it works.
Sometimes, you don’t even need to do this and there are more helpful options. If you get a text with a number that you need to type in to authenticate a login to an app, look in the predictive spelling section of the screen. The number will be there and if you press it, it will be entered into the app.
Also, if you launch the task switcher, you can see more than one app at a time and switch between them. In the example below, although I’m reading the Telegraph, I can also see the results of a Search.