exporting an entire iMessage convo on iMac to PDF

I bought a software that automatically scrolls in an attempt to scroll to the top of a conversation on iMessage on my iMac that goes back two years. It will take a very long time so I'm wondering: is there another way, without having to scroll to the top of the conversation, to export the ENTIRE two year long conversation from the very beginning to PDF? I know you can select a conversation on the iMessage app on the iMac, then File>Print>Save as PDF but that only does like four pages of conversation (obviously does not go back to the start of two years worth of texts back and forth).

If I have to wait for the scrolling software to reach it I guess I will save it as a pdf when that times comes if that's the only way to get the whole thing saved. My computer will be running for a few days, maybe a week, with a couple occasional hiccups I'm sure cause it's a bit older.

I'm also willing to pay money for any third-party app that can do it for you if anyone knows of anything like that. Most stuff I've found can make a pdf file for iPhone convos after transferring it to the iMac, but not just from iMessage texts already on the iMac.