When you see the alert , your operating system or application is telling you that a specific font used in the document is missing. Instead of crashing or refusing to open the file, the software substitutes another font—usually Arial, Times New Roman, or Calibri—to allow you to continue working.

When a program (like Adobe Acrobat, Microsoft Word, or Canva) can’t locate a specific font used in a document, it triggers substitution. It replaces the missing font with one installed on your system—often Times New Roman, Arial, or Calibri.