I have now found a solution to this. I have downloaded the free version of CutePDF and have printed to PDF the old file using these instruction that are in the README.txt document that comes with the download:
Using CutePDF Writer to create PDF document:
DO NOT look for any application to run. Just print your document
using CutePDF Writer (the printer) to get PDF output.
Open your original document and select Print command in File menu
of your application to bring up Print dialog box.
Then select CutePDF Writer as the Printer to print (DO NOT select
"Print to file" option).
You will get a Save As dialog box prompted for saving created PDF
file.
Select a folder to Save in and enter a File name, then click on
Save.
Go to that folder to find your PDF file.
Hope that helps someone.