There is a difference between attaching files in personal and bulk emails. The reason for this is because spam fighters want to protect consumers against malicious content. While your intentions behind file sharing are noble, file attachments on bulk email sends could expose recipients to nasty security risks. The file is added as an html file instead of your original document format to protect recipients against spammers.
So you want to attach a PDF to a bulk email in minutes, here is what you do.

Step 1: To create a secure, easy to access link to your PDF, simply upload the file to your Dropbox account. Once the file is stored in the cloud select the “links” option from the left hand side menu.

Select the PDF you would like to share with your contacts from your list of files stored in Dropbox and click the Widget icon to the right of the image in order to retrieve the link.
While retrieving the link you have the option to edit and adjust your content settings.

Step 2: Now you have the file hosted somewhere you’ll want to add a button to your email linking the file.
In order to direct your recipients to a download link you should include a call to action button. As a marketing best practice the button should be highly visible, clear and appear clickable.

Still have questions? Feel free to send us a message