Link to PDF file (or attach file here):
http://research.microsoft.com/en-us/um/people/hiballan/pubs/ccs08-staledns.pdf

Configuration:
- Web browser and its version: Chrome 54.0.2840.98 (64-bit) and Firefox 49.0.2
- Operating system and its version: Mac OSX Sierra
- PDF.js version: 1.6.210
- Is an extension: no

Steps to reproduce the problem:
1. Open the referenced PDF
2.Try copying text from the article (I've just tried on the first page)
3. Paste somewhere else, and spaces are missing between most words.

What is the expected behavior? (add screenshot)
Copy the text from the pdf with spaces between words: EG first line in paper should copy as
This paper considers DoS attacks on DNS wherein attackers flood

What went wrong? (add screenshot)
This is what is copied
This
paper
consider
s DoS
attac
ks
on
DNS
wher
ein
attac
kers flood

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): Reproduced this using the github hosted version.

I have a pull request to fix this problem in the works.
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