Comment by shadowgovt

You could. But in a thousand page document, that's a lot of memory used up to record a vector for every letter 'c'. So of course you do two layers: record modifiers and transforms on a canonical 'c', and then keep a canonical 'c' somewhere with all the other letters.

... But you already have that data structure: it's the font file itself.

(Possibly worth noting here also is that historically, Adobe owned both the PDF format and the file format for most popular fonts. So they were heavily incentivized to just reuse code they already owned here instead of reinventing a wheel).