How many fonts should ideally be used in a document according to design conventions?

In the context of design conventions, using three fonts in a document is ideal because it strikes a balance between visual interest and clarity. Different fonts can serve distinct purposes—typically, one font for headings, another for body text, and possibly a third for accents or highlights. This approach allows for differentiation of information, making the document easier to navigate and more visually appealing while still maintaining coherence.

Using a single font can result in a monotonous appearance, which might not engage the reader effectively. On the other hand, utilizing more than three fonts can lead to a cluttered and disorganized layout, distracting from the content rather than enhancing it. Therefore, adhering to the guideline of three fonts helps to maintain a professional and aesthetically pleasing design without overwhelming the reader with too many variations.