PLT files traditionally relates specifically to Hewlett Packard printer/plotter files, instead of sending the HPGL or HPGL/2 or PCL code to the printer, it gets saved as a PLT file using the "Print to file" option.
If you are not specifically referring to that format then it is hard to answer the question because each print driver typically has its own language and viewers are not usually made for this type of thing.
For HP PLT files you would need a 3rd party program such as SPLOT (Link)
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