To work with files:
Go into the applicable course
Click the three gray dots in the right corner of the workbook
Choose Edit. This will take you to the workbook builder page.
Select Files
From here you can:
Upload files
Click Upload, select Browse and choose file from your computer
Click Open, then click Upload
The file will now be displayed under the workbook files section and inside your file bank.
See and manage your files
Click Show Bank to view all the files you have ever added, so you can quickly add them to as many workbooks as needed
You can manage your files by clicking the three gray dots next to the file
Click Upload to add more files to your bank
When you go to the PDF Viewer activity, you will see all the PDFs you have added to that workbook.