What is a good substitution for bread flour? Is it necessary? Thank you.

Sorry, I also forgot to add that if you don't have vital wheat gluten, you can just substitute APF and it won't be quite as supple but I'm sure it will still be tasty!

The author probably called for bread flour (which has a higher protein/gluten content) for a reason, because there is so much folding and rolling involved and it will be a little stretchier. If you have vital wheat gluten, you can substitute bread flour for the all-purpose and just add a little bit of the gluten in, to imitate bread flour. I'd only recommend this for flatbread. If you think you might bake any other bread, it's worth getting a bag of bread flour.