If you are facing any issue with Yahoo mail attachments and unable to open it then you should apply these methods to get the solution:
•Try to upgrade your web browser and download the latest version of the browser.
•Also, download the updated Adobe reader program to help you reading PDF attachments.
•Disable antivirus or firewall protection for a while because it may also cause troubles for attachments.
•Now close down all the running programs and restart your computer to fix the issue.

In case of further assistance, you can contact at Yahoo helpline number and get the most prominent support for fixation.