Can you mix Layout Library and Fully Editable pages?

You cannot mix these two design formats because they are fundamentally different and use very different settings.

Your document is either a Fully Editable document or a Layout Library document and these formats are 'burnt in' at creation.

However, you can create a new Fully Editable document that uses the same designs as those found in the Layout Library, with your branding applied and full editing control. This can be done using our Components feature.

You can read more about this here → Fully Editable - Components