From the editor, highlight the text you want to attach the PDF.
Click on the link icon to open the Link dialog.
Select URL under Link Type:
Click Browse Server to open the file browser:
Choose the proper location to upload (i.e. your _files folder).
Select the Upload option, then + Add files
This will open your computer to choose the file you wish to attach.
Choose the Upload button from the file browser and the file will upload.
Choose Select to select the file.
You will then be back to the editor Link dialog:
Choose OK to link the PDF file.