Most of the fonts are coming from the operating system and software like MS Word which you or your customer uses. However, these fonts may not represent the whole spectrum of Unicode encoding standard. Some software is not even Unicode based.
When you import documents into memoQ, memoQ does not touch the attributes for the font which is used in your documents. This can result in poor typesetting of the translated documents, especially if the source and target languages use different scripts. Therefore, the font substitution feature is introduced. You can select the font for your documents to be exported, you can also make a font a default one. Changing the font, memoQ will apply the new font to the documents on export. Your exported documents will have the new font.