Changed PDF images to PNG format.

docs/source/examples_2D.rst

@@ -19,7 +19,7 @@ The geometry of the scenario is straightforward and is shown in :numref:`cylinde
 
 .. _cylinder_half_space_geo:
 
-.. figure:: images/cylinder_half_space_geo.pdf
+.. figure:: images/cylinder_half_space_geo.png
     :width: 600 px
 
     Geometry of a 2D model of a metal cylinder buried in a dielectric half-space.
@@ -123,7 +123,7 @@ You should have produced an output file ``cylinder_Ascan_2D.out``. You can view
 
 .. _cylinder_Ascan_results:
 
-.. figure:: images/cylinder_Ascan.pdf
+.. figure:: images/cylinder_Ascan.png
 
     Field outputs from a model of a metal cylinder buried in a dielectric half-space.
 
@@ -169,7 +169,7 @@ You can now view an image of the B-scan using the command:
 
 .. _cylinder_Bscan_results:
 
-.. figure:: images/cylinder_Bscan_results.pdf
+.. figure:: images/cylinder_Bscan_results.png
 
     B-scan of model of a metal cylinder buried in a dielectric half-space.