I actually asked this question to superuser.com before, and received some answers. However, I thought my question is specific to LaTeX-generated PDF files, so tex.SE people perhaps know better for such PDFs and font problems, etc.
When I read LaTeX-generated PDF files with Adobe Reader or Adobe Acrobat Pro, the display quality is superb. However, for the same PDF files, other PDF readers like Foxit Reader, Sumatra PDF Reader, etc show poor quality: quite timid and fuzzy display. At least in Windows. In Linux systems, any reader is not satisfactory even the Adobe Reader.
Why? Is it because the PDF format is created by Adobe? Is there any LaTeX-font problem for other readers?
Here are some sample screenshots. All viewers are set to zoom to page width.
(1) Sumatra PDF
(2) PDF X-Change
(3) Foxit Reader
(5) Adobe Reader
To me, Adobe Reader clearly is the best. Especially look at the italic capital T.
Here is the sample PDF file.