In order to improve the final PDF text quality, it is recommended to use LaTeX T1 font encoding (LaTeX uses T0 font encoding by default). The difference between T0 and T1 font encodings can be understood by observing the following PDF files:

Although they are visually identical, there are some differences. To see them, try to copy & paste the contents of each file to a text editor, and observe how accented characters are copied.

T1 font encoding preserves accented characters when converting the PDF to raw text; this behavior is important when the PDF file is indexed by search engines, or when copying its contents to other files. Also, LaTeX does not correctly hyphenate words with accented chars when using T0 encoding.

To generate PDFs using the T1 font encoding, these lines should be in the preamble of your .tex source file:

\usepackage{lmodern}       % Latin Modern fonts
\usepackage[T1]{fontenc}   % T1 font encoding

You can replace the lmodern font (LaTeX default shape, equivalent to Computer Modern) by any other recent font with T1 encoding support, like pxfonts or txfonts.