Thank you for reaching out to the Community! If you are needing to send out document or a big file in your email campaign, there are a couple ways to do this. The first option is uploading the document to your Library, and linking it to a button or text within your email campaign. You can click here for the instructions to walk you through the process.
Our Library does have a 5MB size limit, so if your attachment is bigger than this, I would suggest hosting the files online. Once the file is hosted online, you can copy the direct link and add it to your email campaign.
I hope this information is helpful! In the meantime, if you have any further questions please feel free to reach out to us here. We are always happy to assist you in any way we can!