How to find out what font a PDF document is written in?

Use Poppler to view a list of all embedded fonts within the PDF file.
http://poppler.freedesktop.org/

Note that if the fonts aren't embedded they will be substituted with generic fonts meaning the font will change depending on which system you are viewing them on.

avira

I think using verypdf's free font extracting tool will help you extract all fonts used in a pdf file.

You could start by including a screenshot of it.

Or include the actual FULL file name, and a link to the website where you found it.

Then, we could look at it, and suggest what typeface it may be.

Try making a screenshot and upload it to one of many services that are used to do so,

PDF to Word converter maybe?
It will still maintain the same font, so you should be able to read it there.