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:
Note: Sending files from the File Library is only available for groups that belong to a community. It is not available for Independent groups.
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.
3. In the upload window, click Click to upload or drag and drop the file, then choose it from your device (files up to 20 MB). Repeat 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 New folder 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.