Here\'s a link tho what made me start digging into custom Props again.
I can see that my customProperties are 0 so i assume getCount is somewhat working, even though I\'
I verified this code does not crash Word and works. (assuming you are in latest builds, if your items.count works, this should too.
Word.run(function (context) {
context.document.properties.customProperties.add("PropertyName", 1234);
return context.sync();
})
If this does not work, please reply with your build number. thx.