If you make a selection in Adobe Photoshop and try to paste it into Microsoft Word it won't work well (and sometimes won't work at all). Microsoft and Adobe are trying to use OLE (object linking and embeding) a novel concept from the 90's that just doesn't work very well. Once you paste the PhotoShop file into Word it's litterly embeded and you can double click the object to open it back in Photoshop. Nice concept but it doesn't work well. Once pasted in Word you can't do even simple manipulations in Word such as resizing, cropping or anything else using Word.
The file size gets significantly larger because you have now pasted a bunch of extra info into Word and in addition the quality tends to be much lower. As an extra bouns instead of just loading Word you're now loading Photoshop and Word at the same time. Ugh. OLE is pretty terrible and only programs that have been around since the 90's still support it as a legacy thing.
The solution is to copy from PhotoShop, Paste into MS Paint, Copy from MS Paint and paste into Microsoft Word. The extra step is a pain. I've been using this trick for years and every time I get a new version of Word or Photoshop I hope that someone will have fixed this 'feature.
P.S. You can also use Word's 'paste special' to work around this as well but there's nothing special about what I'm doing. Pasting an image without the embeded part should be the default.