7-Zip's LZMA2 algorithm, which significantly reduces large PDF or CAD file sizes.
The .7z extension indicates it was compressed using 7-Zip software. 11DHB.7z.001
These are the most reliable tools for joined volumes. 7-Zip's LZMA2 algorithm
The .001 suffix means this is one part of a larger file. 11DHB.7z.001