Check this forum
related topic.
The current version includes that script, to copy the metadata from the NTFS ADS to the PDFs metadata, as a sample script (check the attached image).
The script copies all the summary information fields (Title, Subject, Author, Keywords and Comments) to the equivalent, and custom for the comments, fields. If you only want to copy the comments you need to edit the script and change the line
FIELDS = ['Title', 'Subject', 'Author', 'Keywords', 'Comments'];
to just
FIELDS = ['Comments'];
The script puts the comments data in a comments named custom field, so you need to have a custom field already defined also named "Comments". Check second screenshot.
Try with a sample file first, to see if it works.