First, be sure the Read&Write for Google Chrome extension is installed.
If you don't see Read&Write for Google Chrome™ listed when you right click on a PDF in Google Drive, click Connect more apps
Then enter Texthelp in the search box and click Connect to add the Texthelp PDF Reader
You can leave Make Read&Write for Google Chrome™ the default app for files it can open if you want it to be the default reader for all PDFs. Untick the box if you don't want it to be the default.
Alternatively, you can:
1. Add the Read&Write for Google Chrome extension
2. Go to Google Drive and open a new or existing Google Doc. This will prompt you to choose an account:
3. Click the Allow button to confirm permissions
4. Go back to Google Drive and refresh the screen (hit F5 or the Chrome refresh button)
5. Then open a PDF. You should now see Read&Write for Google Chrome™ as an option when you choose Open with