In terms of font accessibility, there are a number of principles to keep in mind:
Use real text rather than text within graphics.
Select basic, simple, easily-readable fonts.
Use a limited number of fonts.
Ensure sufficient contrast between the text and the background.
Avoid small font sizes.
Use relative units for font size.
Limit the use of font variations such as bold, italics, and ALL CAPITAL LETTERS.
Don't rely only on the appearance of the font (color, shape, font variation, placement, etc.) to convey meaning.
Avoid blinking or moving text.
Watermarks make it difficult for people with low vision to read the body of text in a document. Additionally, watermarks are not accessible to screen readers; they must be tagged and meet contrast. The best practice is to put information such as disclaimers on a separate page as text.