If you are using Firefox as the browser, go to tools and click on downloads, if you see the PDF you downloaded, then right click on it and look for "copy download link" left click that , you can then go back to the thread and post that in there.
Or you can go to the section down the bottom of the page when you are posting and look for upload a file, when it opens look for the PDF document (if you saved a copy)if you see the file in your documents just highlight that file with a left click and then press open, it should then start to upload, when it is finished uploading you can post your message.
