My LTD provider, one of the big 3 sent me two forms they wanted signed and sent back to them. Once I sent those back they sent my LTD medical file to CPPD. I also got my psychiatrist to fill out the CPPD medical form. I know for me my psychiatrist did a great job on the CPPD medical and that is what lead to my initial CPPD application approval. The two forms the LTD provider wanted was:
SC ISP-2502-B - Consent for Service Canada to Obtain Personal Information (this form allows the LTD provider to send over the medical information to CPPD)
SC-ISP 1606 Authorization to Communicate Information Canada Pension Plan (this allows CPPD once a year to let the LTD provider know how much in CPPD they are paying me)
These two are pretty standard forms, there is nothing to worry about and I would recommend you sign and send back to your LTD provider. Where are you in the process, have you applied or has the LTD provider asked you to apply for CPPD now?