A font is a set of text characters in a specific style. Is recommended to make your fonts around 8-12 pt so they can be easy to read.
A problem that occurs very often when the fonts aren't embeded in the document, is that the style you chose for your designs gets substituted by a default one or rasterized, making it look pixelated. This happens if the computer where your file is opened doesn’t have the exact font you used.
From time to time, any type of font can have a problem. To 100% avoid substitution or raster in your fonts, the least you can do is embed the fonts to your file, but we recommend to outline your text (Illustrator) or flatten the image (Photoshop).
Go to Type>Create Outlines
Layer Options>Flatten image
Keep in mind that after outlining your text, you will no longer be able to edit what it says, so you should keep a backup file that you can edit in case you need to make some changes later on.