There are some minor differences between the PDF instructions and the LDD file. Please refer to the PDF for the parts list for the PDF, currently the site's parts list refers to the LDD file. I will update and remove the LDD file in the future, but I need to proof-build the model to make sure everything is okay in the PDF (I looked through it, but an actual build might reveal some mistakes).
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These types of files are created with the LDraw system of software. You will need to install compatible software to open and view the instructions.
A full list of available software is on the LDraw site.
This MOC also has a LEGO Digital Designer file available: 3D Model