import urllib2

from reportlab.pdfgen import canvas
from reportlab.lib.pagesizes import A4

pngdata = urllib2.urlopen('http://images.wikia.com/history/ru/images/c/ca/Roman_Empire_Map.png').read()
open('map.png','w').write( pngdata )

c = canvas.Canvas("map.pdf")

lWidth, lHeight = A4

c.setPageSize((lHeight, lWidth))

c.drawImage('map.png', 0, 0, preserveAspectRatio=True)
c.showPage()
c.save()