i could not find the answer how to create "comment" box from contact sheet. I create contact sheet from lightroom using print to pdf. Then what about client to make comments on each photos. How?
Getting comments on Contact sheets is not Possible.You can have Shared Collections and using Albums/Publish services(like Facebook,Flickr etc) can get comment on each Photo individually .See Creating Contact Sheets with Lightroom Collections
This is how you can have comments on your Pictures Adobe Photoshop Lightroom Help | Share photos for comments and feedback
For someone to be able to comment on PDF's they will need Adobe Reader Product.See Adobe Reader X * Share, comment, and review