When assigned PDFs are annotated and returned by students they will appear in the Classroom Student Work window
To open PDFs with the Texthelp PDF Reader, click the Open folder for assignments icon above the turned in assignments
This will open the folder in Google Drive
Click on a turned in PDF. The PDF will then open in the Texthelp PDF Reader
Once you've opened the PDF you can return to the Student Work window to grade the assignment
If the PDF opens in the Chrome Preview window, then click Open with > Read&Write for Google Chrome™