When you download a free PDF from NAP.edu, we display an optional comment box that allows you to write a comment about how you're using the publication. The comments aren't displayed publicly, and are used by individuals and groups at the National Academies for qualitative analysis. That is, we only use them to understand how you are using the reports you're downloading.
Absolutely no private information is made available. We do not share your email address with anyone, we will never sign you up for an email list (even lists of the National Academies) that you did not explicitly choose to sign up for, and your comment itself will never be distributed publically unless you've given us explicit written permission.
Additionally, your comment will never be associated with your email address, so even those people who do have access to the comment you leave will never be able to see the person who left it. If you would like to be personally identifiable to the people who read the comment, you can leave that information in the comment itself.
Occasionally, groups inside the National Academies will aggregate comments to report to sponsors or in publically available impact reports, but the comments themselves will not be distributed. Instead, the information will only be communicated as grouped in similar types, i.e. "7 downloaders of this report indicated that they would use it for personal research."
Leaving a comment is entirely optional, but we would like to emphasize that knowing how people use our freely-available reports is vital to our research efforts. We encourage you to leave comments when you download to help us better understand their use.