Hi Oms,
Attachment of files isn't supported in the Marketing emails, which is by-design.
And outbound marketing only allows you to upload image files.
https://learn.microsoft.com/en-us/dynamics365/marketing/upload-images-files
1.One possible workaround is to create images of the PDF file and you can embed those in the email.
2.If you use real-time marketing, it supports other file types, not just images.
The centralized real-time marketing asset library lets you upload images, videos, and documents.
The asset library supports images (such as JPEG, GIF, and PNG files), videos (such as MP4, AVI, and MPEG files), and documents (such as Word documents, PowerPoint files, and Adobe PDFs).
https://learn.microsoft.com/en-us/dynamics365/marketing/real-time-marketing-asset-library
Then you can select the uploaded file in one button of the email:
https://meganvwalker.com/adding-file-download-to-a-marketing-email-button/
3.Or you can create one workflow to send emails(You can attach files you need), then add the workflow to segments:
https://www.linkedin.com/pulse/sent-attachments-dynamics-marketing-vincent-groenheijde
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If you insist on adding attachments in the marketing email, you can create a new idea through the below URL, then ask your colleagues to raise up the votes.
Ideas (dynamics.com)
Our product team has direct visibility of these ideas and they will implement it on the basis of the highest number of votes received.