Convert the pdf to an image file, then you can import it

Note that you can't import an arbitrary image and expect the data points to line up. You can stretch data points across the map using a linear transformation, but this only works for small areas where the map projection is effectively linear. Otherwise you will need to either use the world map or place the markers yourself inside Omniscope.

Basically i have a pdf of the proposed high speed rail network and would like to plot postcodes on this map so i can see how/close far each postcode is from the proposed route.

Any ideas on how i either convert pdf to one of the associated files etc ?Or another option to which encompasses the above idea ?

If it is UK data, you can use the OS Easting and Northings values then plot those using the linear transformation. You can get those values using the convert functions

CONVERT_LATLONG_TO_OSGBX
CONVERT_LATLONG_TO_OSGBY

The OSGB values will be effectively linear so it will fit nicely over a flat imported UK map when you apply the transformations.