I have tested this option but have difficults to have the proper function.
If a co-author recieves a link to the document that the author has shared with him.
What is the mechanism that hinders this person to read that file that the co-author has send him.
I have been playing with myself in diffrent roles but running out of mail adresses and understanding.....
Please give an explanation.
In the sharing dialog (where you enter the email addresses) there is a link at the bottom that says "More options". This is where you can adjust the re-sharing options. Default is "Everyone the file is shared with can share it with others (at their own role or lower). The other option is "Only let co-authors share this file with others."
After the file has already been shared you can change the sharing options by doing the following:
Co-authors have the same rights as an author and there is currently not a setting to prevent co-authors from sharing. If they do not need to have the same rights as an author, try changing them to a reviewer or reader and changing the share option to "Only let co-authors share this file with others."
You can find more information about the different roles here.
If I've misunderstood your question, please post again.