Is there a difference in "opening" a file from the file manager and "downloading" a file? May be a better way to express the question is, when I "open" a file using FileManager does it first download the file to my computer and then open it? If it does download it first where is it saved and when I close the file is it deleted from my computer.

The bottom line is that I want to see a file from my computer but I do not want to download it. I just want the file to be displayed on the screen.

Thank you.

Opening a file from File Manager does indeed download it to a cache folder.  You can find this cache folder by going to Tools -> My Options -> View Cache Files.  Is there a particular reason why you do not want to download?

I also want to be able to have a customer I am sharing a file with to not be able to download it, only view it (pdf files in particular).  These files have company sensitive info that we need to restrict copies of it being out there.

Sorry, but there is currently no way to set that type of permission.  Generally, if a user is able to view the file on their computer, it has already been downloaded.  It is very difficult in any scenario to restrict a user to not saving a file on their computer.  It is advisable to inquire about your question with Adobe; it is possible they may have a solution to induce an unsavable file.