You may want to backup iMessages for various reasons. There are three formats to save iMessages with iBackup Viewer.
PDF is the most popular and standard file format to present rich content documents, including well formatted text and images.
And, the most advantage of PDF file is maintaining the native style as of Messages.app, including photo attachments, which makes PDF format the best option to backup iMessages of iPhone. With iBackup Viewer, you can easily export iMessages to PDF files from iPhone backups.
Here is a step by step tutorial to save iMessages to PDF:
Launch iBackup Viewer after installation.
Open the backup by clicking the backup icon.
Click on "Messages" icon to open messages
Enable options to Save photos in PDF in Preferences
Save iMessage to PDF
Options for PDF output
Advanced options for messages output
Click "Save" and choose a folder to finish creating iMessage PDF file.