If a document uses fonts not installed on your system, you see an alert message when you open it. Photoshop indicates which fonts are missing and substitutes missing fonts with available matching fonts. When this happens, you can select the text and apply any other available font.

Glyph protection protects against incorrect, unreadable characters that appear if you enter non‑roman text (for example, Japanese or Cyrillic) after selecting a roman font. By default, Photoshop provides glyph protection by automatically selecting an appropriate font. To disable glyph protection, deselect Enable Missing Glyph Protection in the Type preferences.