This text is almost unreadable to me. The characters are actually touching one another, blending together.
If anyone wants more punishment, the rest of the document is here: https://ista.org/docs/1Aoverview.pdf
Also, relevant xkcd: https://xkcd.com/1015/
Usually due to the use of a non-standard font without including it in the PDF. The viewer substitutes the font with the closest it can find. The glyphs’ spacing remains from the original font, though.