The easiest way to send your seating plan to your caterer is to email the plan file. They can download a free version of PerfectTablePlan to look at it (they will need a licence to save changes). Alternatively you can export and email the information they will need in a range of formats.
Total numbers and meal choices
You can print or export this information from the 
Statistics pane (note that meal courses and special requirements will be totalled separated if they are separated by commas, e.g. soup,fish,flan). Use File>
Export and select statistic to text/CSV/HTML file to export an HTML or text file.
General layout, size and shape of tables
You can print or export this information from the 
Floor plan pane. Use File>Export and select Floor plan to image file to export an image file.
Who is sitting where, meal choices and special requirements
You can print or export this information from the 
Table chart pane or 
Table plan pane for each table. Ensure the notes, special and meal information is displayed. Use File>Export and select table chart to text/CSV/HTML file to export a text, CSV or HTML file. Use File>Export and select Table plan to image file to export an image file.