Layout Of A Document
Foreword: create simple layouts for end users
The difference between a "classical desktop-publishing file" and a file aimed to be uploaded to an print customization platform is that, in the second case, you must, as graphic designer, prepare a file that will be handled by other people, most of them completely unaware of graphic design (the "final users").
Good practices when preparing a document: do not leave anything useless, go straight to the important and build your document in accordance with standard practices, even if it may spend more time preparing it.