Looks like it can be opened only, like:
(startapp "pc3exe.exe" (getfiled "Specify pc3 file" "" "pc3" 0))
or using the shell app:
(defun _openfile (file / sh)
(if (findfile file)
(progn (setq sh (vlax-get-or-create-object "Shell.Application"))
(vlax-invoke-method sh 'open (findfile file))
(vlax-release-object sh)
file
)
)
)
But its kinda sad that activex won't do the job.