We do not file calibration certificates in the TMF. We ensure that the CRAs are verifying that the site has calibration certificates when they are on-site and then documenting that in their visit reports. I look forward to hearing how others have handled this. Thanks!
Typically those files are hard to read when printed, so we usually keep the files on a USB or flashdrive in the TMF (if using a paper TMF). I look forward to hearing what others have been doing.