iBackup Viewer always supports to export iMessages and sms messages to pdf natively on Mac, but it did not supports so on Windows, you were required to install 3rd party printing software like PDF Creator to do such exporting work. But now, the windows version supports saving iMessages and SMS messages, even WhatsApp messages to PDF files easily following these simple steps:
After you install iBackup Viewer on windows, you can run it from "Start" menu or desktop
Find the backup you want to export messages from, and then choose "Messages" in the left side panel to show the messages.
Locate the message thread you want to save to pdf file, and then click the "Action" button on the top right of the window, then choose "Export PDF..."
You need to specify a font for saving the pdf, so that the file can be viewed on different computers. Also, you can choose to give it a password to make the pdf file encrypted to protect your privacy.
The file will locate in the folder you specified in last step after confirming the font and password if it is enabled.