You can attach files to any post or reply. In the post submission box click Insert.
In the pop-up menu, click Image/video/file.
In the new pop-up window click Upload. Please note the Upload text is gray and does not look like a clickable link, so it is easy to miss this step. You must click it to attach a file.
In the pop-up window, navigate to the file you want to attach and select it, then click the Open button.
On the next screen click the Ok button.
Your file will be attached to your post or reply. Click the Post or Reply button when you have finished typing any details you want to include in the post.