Steps to reproduce the issue:
Create a task form in APS adding the "Attach file" component
Create a new task after the previous one, including the "Display value" component mapped to the "Attach file" Form Id.
Save the workflow, deploy the App & run it from ADF. Here is the ADF component used :
Add a file in the first task (doesn't matter if it's stored in ACS or in local). Please make the tests with a docx file or something like that, because it seems that PDF file preview is not working the same way.
Finish the task and go through the second one.
In the second task, click on the actions button presented side of the file then click on "View".
File attached preview opens in browser when user click on the "View" action from a task form.