Proofreading is reserved for finalizing a manuscript that has already been laid out. A layout is set in PDF form and it isn’t directly editable. If you are working with a word document or still making significant changes to the manuscript then line editing or creative development is a better choice. If you have an existing layout from another provider, make sure you have the indesign package as well since you can’t edit a PDF. Proofreading is less expensive than line-editing because it represents “finalization.” It is usually one-directional. The editor finalizes the layout and sends it to the author. The author reviews the changes and can add their own using proofing marks. The layout is returned to the designer who implements everything. The classical editing experience of discussing things with an editor and making suggestions for changes is line editing. Proofreading is necessarily limited in order to finish the manuscript as it is. Editing processes have an order and you might think of building a house. Manuscript review and creative development are drawing up the blueprints. Line editing is building the walls and roof. Proofreading is painting. A manuscript might not be ready for proofreading just because of the state of the draft. A manuscript that needs a lot of work or needs a lot of help should be in line editing or creative development.