I think there are another way to save PLC program as .ACD file, but smaller than normall saved, because I see somebody did it, but I forgot how to do it.
Suffice it to say that since its a structured storage file it may be much larger than it really needs to be. You can do as bguinn says and save it in an L5K format but that might be a pain to work with. You could try saving as an L5K and then importing the L5K and saving as a new ACD file; the new ACD file might be smaller since it doesn't have any old stuff left over in the structured storage file - I haven't tried it though.
Personally, unless you're facing problems transporting the file, I wouldn't worry about it.
It is what it usually does with large files. You must have faith... We usually start the function before we leave work. It is usually done when we come back next morning.
just trying doing a "File/Save As" operation - but give the file a new (different) name ... if that works OK, you can always use Microsoft Windows to "rename" the file later - even back to the original name if you want to keep things straight ...