A client sends an editable PDF but all text appears as "F1", "F2" in Adobe Illustrator. You don’t have their original Asian fonts. Repacking converts the CID subsets to outlines (while preserving the text as invisible metadata for searchability) or merges the subset into a usable temporary font.

There are three main ways to handle a repack, ranging from brute force to surgical precision.

But what exactly are these F1-F4 fonts, and why are people "repacking" them?