I want to give a .pdf copy of book I wrote to a business for their use. I would like to insert a water mark or some other kind of visible notation on the pages that "this copy is for their use only"
Others may reply with other suggestions, but here is how I would do it.
First, open the master page (or one of them if you have more than one master page). Create a large text frame in the middle of the page. Set the font for the frame (with the Properties Palette) to a very large point size of a font that has a "black" version, preferably a sans serif font. Type your watermark or copyright information in the text box, center it and/or apply other tweaks so it looks the way you want it to appear on each page. Finally, set the color of the text to 10-20% black (or pick an appropriate gray color from the palette).
If you have more than one master page copy and paste the text frame onto all of them.
Your watermark will now appear on all your pages. If it is too dark for your text to be readable through it, go back to the master page(s) and change the font color to a lesser percentage of black.
If you want you can also rotate the text frame, say, about 15-20 degrees for an additional effect.