Some people, especially in PowerPoint, are using (too) many fonts and exotic fonts that they use on the slides.
There are some very general fonts like Arial, Courier and Times New Roman. A common problem is the lacking of fonts that you used on your original computer, that are not present automatically on other computers. On the second computer, your document or slides are looking differently.
You prepare a nice Word document or PowerPoint document and you open it on another computer or send it out to someone else.
