scanned image as background

I swear I've done this a long time ago, and thought it was simple, but
for some reason I'm having a problem with this.

Have a scanned pdf form, and want to use it as background on a Report
(of as background on a Form and just print the Form would work also)
where would simply place the text boxes on top of the background in
the appropriate places and print it out that way.

Should be simple as can be, but every time I tried to insert a
background, it came in as an object rather than a simple background.
Does the file format matter? Such as has to be bmp or wmf or can it be
jpeg or tiff?

thanks