From the Group Message Center you cannot add an attachment to a message. However, you can send a file from the Group File Library, and that process is very similar to the Group Message Center. Just follow these steps:
1. In your group go to File Library.
Do the next 2 steps only if your file has not already been uploaded to the File Library.
2. Create a subfolder, or upload your file to the main folder by clicking Upload File.
3. Click Choose File and find the file on your device you want to upload. Next, click Upload. Repeat these two steps for each file you want to attach.
4. Find the file you want to attach the check the box next to that file for Send File(s). Note that you can check multiple files if you'd like to attach more that one file.
5. Click the Send File(s) button at the top of the page (next to the Create Subfolder button).
6. You will now see a screen that looks very similar to the Group Message Center. Fill out the fields and send your message. Your files will be automatically included as links at the bottom the message.
Note: Do Not Remove "[The file(s) will appear here]" from your message, otherwise your files will not be included.