Adobe Acrobat 8 has a text smoothing feature that causes text to virtually be unreadable with black blocks around it when using a terminal session. The issue does not appear in older versions of Acrobat. Sometimes the issue is resolved by increasing the number of colours for the session that you are running – try 16-bit or 24 bit.
What we have found resolves the issue is by turning the text smoothing off altogether. You can do this through the registry