Portable Laser Format
|Type:||laser project file (custom zip container)|
PLF is just a ZIP file containing the source graphic files (SVG, PNG etc.) and some xml files containing VisiCut's settings. You can just rename it to .zip and then open it. It does not contain any information on the laser cutter, nor the code which is sent to it, because that code is generated on the fly once the laser cutter has been selected in VisiCut.
(from on the corresponding VisiCut wiki entry as of 2016-11-7)