I have been using my computer to generating pdf files from latex file by Winshell (or lyx), but the characters (or images) in the pdf files generated on my computer looks always much worse than the pdf files other people generate on their computers. Could anyone tell me what the problem is, or how to improve the quality of pdf file to be generated on the my computer? (I am using the newest version of Adobe Reader, and the miktek files are almost complete.)
This FAQ answer discusses a number of reasons why the PDF quality may suffer.
The testflow package can also help with diagnosing such problems.