If you are not able to view PDF attachments in Gmail, then to get this problem fixed first of all get the add ons disabled for that open your browser then click the “tools button” further click on “manage add ons” then click on them one at a time in order to get all of them disabled after that get them re-enabled one by one and see which particular add on is creating the issue so that you can get that particular add on disabled, the user can also fix the problem by conducting a reset of the web browser security settings and ​If you need any further assistance then ask for it at Gmail helpline number UK & http://www.gmailhelpline.co.uk/