iMessage/sms

You can transfer all your messages to PDF or txt files with inexpensive software for your Mac or Windows computer. E.g. search for PhoneView or iExplorer.

Do you have access to your Messages account on a Mac?

Select the thread.

File > Print

Ok

• Double click on the chat that you want to export
• Scroll to the top, or wherever you want to start from
• Command/P (or click on file and print)
• Select "Save as PDF" from the drop down
• Select where you want to save it to
• Voila...you have a pdf of the whole conversation

The key is scrolling up to where you want to start from.

Hope this helps

Apple does not have a tool for this, but an internet search might find you a 3rd party option.