If you need a for a specific missing font, you’ll need to know the exact font name (e.g., Helvetica, Futura). Let me know the font name, and I can guide you to a legal source or alternative.
Getting the warning means the document you are opening uses fonts that aren't installed on your current device. If you click "Continue," your software will automatically pick a similar-looking font to replace the missing one, which can shift your layout or change how your document looks. Download Font Substitution Will Occur Continue