Indeed, that is the Kerning code.. but it isn't working. Someone else I know has got the whole thing working, and they didnt have to change anything. However, somehow using the same ttf file as they are, the kerning is not being applied
I looked at the docs for PDF::API2::Basic::TTF::Kern, and it seems that it'll read and output to file information on kerning tables 0 and 2. There are no support functions that do anything with the kerning tables at this time. The author calls it a "bug".