Find a PDF renderer such as Ghostscript, and use it to render the signal into an image. Then use one of the various File Exchange contributions to "digitize" the image. Search for tag:digitize inside the File Exchange.
You might get lucky and all the needed coordinates might happen to appear in sequential text form inside the PDF, but most of the time when they appear at all they tend to appear in some messy order, and it would be common for them not to appear at all in text form.
