Size and shape :at your discretion, remember the viewer will be on a computer but like all pdfs they will be able to control the scalling.
How to do this:-
Log on to your Booking system account (where you submitted your abstract)
You should see 'view details' click on this
click on 'Go to your abstract' then click on 'Edit' next to the title of your abstract
Click on the Attachments TAB.
Then select the file and upload.
An example of what they look like is here:https://www.myeventflo.com/brochures/Poster0023240.pdf