Access the bulk messaging templates via Applicants > Send Messages. Click New Message, or click the name of the template you would like to edit.
Click on the Insert image button. Copy and paste a link to the image into the pop up box, and click Insert image.
Scroll to the bottom of the bulk message page, and click on the + Add File button. Then click on the Browse button. Select your file, and click Open. You can attach multiple files to one message. If you would like to remove a file, click on the red trash can icon to the right of the file.