: Select "7-Zip" > "Extract files..." or "Extract Here." 7-Zip will automatically detect the other pieces and reassemble the original file for you.
: You cannot open "piece .008" individually; the decompression software needs the header information typically found in the .001 file to understand how to put the puzzle back together. UK-PD Plan.7z.008
The file is the 8th segment of a multi-part compressed archive created with 7-Zip . : Select "7-Zip" > "Extract files