It allows you to take a jpg and exctract the co-ordinates of any points you want (digitising).
I've just been playing around extracting the lines from a jpg of a boat based on a jpg picture downloaded from the web.
It certainly beats measuring by hand from a paper print!
I used it to generate an xml file containg the data points (in pixels), read that file into a spread sheet, then from known points on the print you can apply the offsets & scaling to create the X,Y value you need.
I actually allowed for X & Y scaling to be different (to allow for stretch when scanning the original) and also allowed for a small tilt in the X (horizontal) axis all within the spreadsheet.
I think it can do the scaling itself as it asks for min/max X & Y to start with, but the output files contains the raw pixel co-ordinates as well.
One evening on the PC and I have the basic pressure hull for C class :)
You do have to have java run-time environment, but thats also a reasonably simple job, and your PC may have it anyway as its used by many apps now.
not sure what other image formats it accepts, but pdf aint one!