I took a quick search through the Registry and found the associations for the .c2d file extension and a shell open setting.
There is a settings.ini in the %AppData%\Local\Carbide 3D\Carbide Create
[General]
gridSpacingInch=6.35
recentFiles=C:/Projects/Mirror/Grammy/Grammy.c2d, C:/Projects/Mirror/Starvish/Starvish.c2d, C:/Projects/Mirror/RobinJohn/RobinJohn.c2d, C:/Projects/Mirror/Mimi/Mimi.c2d, C:/Projects/Mirror/MikeCorrine/MikeCorrine.c2d
pos=@Point(289 157)
size=@Size(1920 1009)
windowGeometry=@ByteArray(\x1\xd9\xd0\xcb\0\x3\0\0\xff\xff\xff\xff\xff\xff\xff\xf8\0\0\a\x80\0\0\x4\b\0\0\x1"\0\0\0\xbc\0\0\x5)\0\0\x3\xed\0\0\0\0\x2\0\0\0\a\x80\0\0\0\0\0\0\0\x17\0\0\a\x7f\0\0\x4\a)
lastFolder=C:/Projects/Mirror/Grammy
lastFileMM=false
lastWidth=254
lastHeight=304.79999999999995
lastThickness=12.7
lastModelResolution=0
lastZeroX=0
lastZeroY=0
lastZeroZ=0
lastMachine=Shapeoko 5 Pro
lastMaterial=Hard Plastic
retractHeight=1.27
lastTool=“{"angle":0,"corner_radius":0,"diameter":6.35,"display_mm":false,"finish_allowance":0.508,"flutes":2,"length":19.049999999999997,"model":"251","name":"","number":251,"overall_length":3.175,"plungerate":304.79999999999995,"read_only":false,"slot_depth":1.016,"slot_feedrate":1524,"slot_rpm":18000,"surfacing_feedrate":1524,"surfacing_rpm":18000,"surfacing_stepover":10,"type":0,"url":"https://shop.carbide3d.com/products/251-25-downcut-flat-cutter\“,\“uuid\”:\”{00000000-0000-0000-0000-000000000000}\",\“vendor\”:\"Carbide 3D"}”
lastFont=MV Boli
lastBackgroundFolder=C:/Users/sewsk/Downloads/Horse2a.jpg
lastImportFolder=C:/Projects/Mirror/Grammy/GrammyTemplate.svg
lastImageFolder=C:/Projects/Sean/barnCrop.png
extraVolume=0
volumeUnits=1
lastRectangleRadius=12.7
lastPostProcessor=:/r/resources/posts/shapeoko.post
lastPostProcessorMetric=false
lastOutputFolder=C:/Projects/Robin1/test3dRough1.nc
lastCutDepth=0.254
lastVeeTool=“{"angle":45,"corner_radius":0,"diameter":12.7,"display_mm":false,"finish_allowance":0,"flutes":2,"length":6.35,"model":"301","name":"","number":301,"overall_length":3.175,"plungerate":304.79999999999995,"read_only":false,"slot_depth":2.032,"slot_feedrate":889,"slot_rpm":18000,"surfacing_feedrate":889,"surfacing_rpm":18000,"surfacing_stepover":2,"type":2,"url":"https://shop.carbide3d.com/products/301-50-v-bit-cutter\“,\“uuid\”:\”{00000000-0000-0000-0000-000000000000}\",\“vendor\”:\"Carbide 3D"}”