In all probability you can't. This is something which really needs to be
done using a capable graphics editor such as Photoshop where you can create
what is called a 'clipping path'. Word's convenience tools do not provide
that kind of capability - nor do most programs which offer an array of
graphics features secondary to their purpose.
One thing you can try is the Transparent Color tool located in the Picture
group of the Formatting Palette (Toolbox) which appear when a picture is
selected. When you select the tool click in the part of the image you want
to have rendered transparent. The limitations of the tool are;
1- It can be used on only one color in any given image. In many cases what
appears to be 'white' for example may actually comprise a pixels of various
brightness levels so you may wind up with artifacts you can't remove, &
2- All pixels of that brightness level will be rendered transparent
regardless of what part of the picture they may be located. IOW, if the
pixel you click is white all white pixels in the image will render
transparent, not just those in the peripheral area.
But depending on the composition of the logo it may be effective.
HTH |:>)
Bob Jones
[MVP] Office:Mac