There are several synonyms that can be used instead of the phrase "add notes to." One possible option is "annotate," which means to make comments or notes on a text or document. Another synonym is "mark up," which refers to adding notes or highlighting important parts of a document. "Append" can also be used to indicate the addition of notes to a document, while "supplement" and "augment" both suggest adding additional information or details to a text. Other possible options include "jot down," "scribble," "record," and "comment on." The specific synonym chosen will depend on the context and the writer's intended tone and emphasis.