Thanks Freddy and Dutch for your help. That definitely answers my question---though I will have to wait until tomorrow, to test it. Too many things to do today. Yes, I have been away for a while, busy with other things, like household repairs and doctor appointments.
I do already have a working "File Open" dialog box. Like you though, I tend to go more with the old-school methods. I use the dialog merely to get the file and path string. I then use that string to open a file with more traditional methods. I will try to post my code, once I get the file-type filter working.
From my best guess, that appears to be a pointer to a pointer. At least, it seems to behave that way. Or, it could be a way of addressing the processor's physical memory directly, rather than the standard Windows "virtual" memory. I can't really say, as this COM stuff is all voodoo to me.
I'll try to check back in a day or two. Right now, I need to run over to a buddy's house, to help with a small electrical problem. Luckily, it appears that the Microsoft documentation is again up and running. They must have been changing servers, as all of the "IFileDialog" pages had been down for days.