First of all I really like SumatraPDF. It’s fast and lightweight.
Now the problem. I used SumatraPDF to open the following file:
I found that all the horizontal lines in the fractions do not show up. See for example the equation at the bottom of p. 2. I used Adobe Acrobat Pro to open the same file. What I found is that the lines show up but are very dim. However, Foxit reader displays the lines very well. I wonder what the problem is.