Share Private (Personal) Content Files in Chatter

Share private content files (previously known as personal content files) in Chatter. All content files, whether in a library or not, can now be shared in Chatter.
Select a file from Salesforce

When you use the Select a file from Salesforce option to attach a file to a post or comment in Chatter, you can now choose a file from a private (personal) library.

Private Library Files in Chatter