One way is to copy a word from that part of the PDF document, and paste it into Word or another rich text editor. Then click in the middle of the pasted word. The editor's font display will show you the name of the font.
There is a Lin/Win/Mac font tool here http://www.foolabs.com/xpdf/download.html
Many PDF viewers will list the fonts used. Acrobat at least used to do this.
pdffonts, part of poppler-utils, will dump a list of font names.
Take a screenshot and run it through https://www.myfonts.com/WhatTheFont.