It's hard for me as well, looking at the code with blinders on, guessing what is on either side of the snippets.
I'm working off the expectation that the most recently revealed snippet, where you add the row of PDFDocument info to data (PDFCheck.data?) looks something like this, merging what you have revealed to my pseudo code:
See how errorMessageArrayList error messages would be in parallel to data? So the index of the one (the same as the index to your JTable row, unless you're sorting or filtering - if so, adjust accordingly) is the same as the index to the other?
It looks like in your latest example you stuck all the error messages into the content error column and then you pull them out from the JTable to create a JTextArea with just that row's error messages. Is that working for you?