PDFCrop: Is it integrated into Latex? Is it part of the graphix package? What on earth is it?

pdfcrop is is a command that you run to edit the pdf, you do not call it from within latex. It will be one of the commands installed when you installed tex.

But for your use case you probably do not need to edit the pdf file with pdfcrop, just display part of the original.

so for example

documentclass{article}

usepackage{graphicx}

begin{document}

fbox{includegraphics[width=5cm,clip]{duck.pdf}}



fbox{includegraphics[viewport=900 450 1200 750,width=2cm,clip]{duck.pdf}}


end{document}

Includes a complete pdf file then includes the same file just showing part of it. there is no need to use pdfcrop to crop the file.

PDFcrop can be useful if you need to automatically guess the cropping region based on the white space. If so just use a command such as

pdfcrop original.pdf new.pdf

to make a new pdf file, there are several options, see pdfcrop --help

Instead of pdfcrop, you may want to try briss (http://briss.sourceforge.net/), which has a graphical user interface. Open the file, mark a rectangle around the image and click crop.