Some, especially older, documents produced by TeX don't use the today-common vector format for fonts, but rather store them as bitmaps. In the past this had several advantages, such as fast processing and easy rendering. However, the biggest disadvantages are fixed resolution, the inability to precisely scale the font glyphs and to perform antialiasing. Vector format has no such problems and is understood by any modern computer or printer; with proper hinting it can be rendered on screen as precisely as bitmap fonts can, and it can be rendered at any resolution. There is no excuse to use bitmap fonts today.
When rendering a bitmap font on screen, all sorts of rounding or positioning problems can arise, because the only information available to the renderer is a fixed size pixel matrix, which does not scale or rotate well.
With all this said, my advice is to never reproduce the given example, and always use vector fonts. See also Why are Bitmap-Fonts used automatically?