I have just started having this issue very frequently. We have been publishing a series of books that we are trying to get endorsements from professionals in the publishing industry. We have been sending interactive PDF e-books which are not very large files, not much other than text, a TOC with navigation and front and back cover images (nothing really fancy) and half the people we send them to can open them, the other half cannot. We are emailing them from multiple email addresses, Dropboxing them, etc to just try to get them uncorrupted to people. These are people who know how to handle PDF documents too, so it ends up being us that look like schmucks. Has anyone else had this issue? We can open them fine, there are no security restrictions on them at all so that is not the problem. Like I said, some people can open them but others (who have all Adobe programs, creative designers who deal with PDFs all day) cannot. I am baffled as to what is happening and I am looking for a solution. Any ideas?