The pentagon papers were released in 2011. A wikipedia search would have found the complete set at the national archives: https://www.archives.gov/research/pentagon-papers.

I believe they wanted to keep this secret not because it hurt us to leak some secret, it was to hide the fact that every president from Truman on had lied about their actions to get us more involved in vietnam. It's still pretty shocking today. Read the wikipedia page for more info.

I don't think it will happen, but I'd be happy if Obama were somehow able to legally forgive Snowden for his whistle blowing also.