Usually this happens when eMAM doesn’t have access to the PDF proxy. Please check the below steps to troubleshoot this.
1) Open IIS of eMAM Web server. (Where we have the virtual directory for eMAM Director)
2) Check whether the eMAM Director Application have necessary permission. To check this, click on the eMAM Director Application and from the right panel of IIS click on the basic settings.
3) Now click on connect as, and there select the specific user option and give the credentials of an Admin user.
4) Still, if the issue persist, go to Application pool and find out the application pool for eMAM Director.
5) Click on the pool and click on the advanced settings from the right panel side.
6) Now, click on identity and set a custom account.
Please try to take the PDF preview now.