Do you have Ghostsript installed, 32-bit or 64-bit depending on the version of XnConvert you are using?
XnConvert will only process the first page of a multi-page PDF, I think. If you need to process the images in a multi-page file it would be necessary to extract the images in the PDF file to a folder and then process them as images in XnConvert.
If XnConvert won't open even the first page of your PDF file, could you upload an example file (1MB max) that won't open?
You need GhostScript http://www.ghostscript.com/download/gsdnld.html installed to open PDF files using Xnview software, 32-bit or 64-bit according to the version of XnConvert you are using.
Your file opens with XnConvert 1.55, I haven't checked with 1.60 but it should be the same.
Edit:
XnConvert opens PDF files using a default DPI value of 300, this value can be changed if necessary as follows:
XnConvert_Settings_DPI.png (13.23 KiB) Viewed 1816 times
In general, higher DPI values produce higher quality images but also larger file sizes.
Last edited by cday on Thu Feb 06, 2014 10:22 am, edited 1 time in total.