Converting .pdf to an .png file

I would like to convert a portion of a huge 10 MB PDF map file (MN zipcode map with legislative districts)
to an image file (.png or .jpg ).  Small image of original map    Link to huge pdf

NOTE that the automatic scaling of images that browsers do can complicate comparing these images.
With the Firefox browser, the cursor on an auto scaled image becomes a magnifying glass with a
plus sign to indicate that clicking on the image will display it at full scale.

I only want a rectangle of about 10% of the area of the original map (I'd like an image of about 80%
of the metro map inset)

Today I experimented with creation of an image file from a the huge PDF map file.
One crude way to do this is by displaying the file in a PDF viewer and using screen capture.
(The image includes artifact of extra set of scroll bars captured, these could be cropped off but I have not.

I can get the area I want at a lower resolution than I need

Or I can get the resolution I want but with a smaller area

I just discovered Zamzar.com today.  A great service that converts file
formats including PDFs to .png .   But alas it does not quite do the my task.
The  The image file converted by Zamzar from the huge PDF is 2.8 MB:
If I crop it I could get close to what I want.  But it has lower resolution than I need.
Compare cropped Zamzar converted file (cropped to approximate scale of best screen capture for comparison of resolution)
To resolution I want but with a smaller area made with Screen capture