You can use the ImageDrawText function to create a text image in ColdFusion and apply the image as a watermark, as the following example shows:

<!--- Create a blank image that is 500 pixels square. --->
<cfset myImage=ImageNew("",500,500)>
<!--- Set the background color for the image to white. --->
<cfset ImageSetBackgroundColor(myImage,"white")>
<!---Clear the rectangle specified on myImage and apply the background color. --->
<cfset ImageClearRect(myImage,0,0,500,500)>
<!--- Turn on antialiasing. --->
<cfset ImageSetAntialiasing(myImage)>

<!--- Draw the text. ---> 
<cfset attr=StructNew()>
<cfset attr.size=50>
<cfset attr.style="bold">
<cfset attr.font="Verdana">
<cfset ImageSetDrawingColor(myImage,"blue")>
<cfset ImageDrawText(myImage,"PROOF",100,250,attr)>

<!--- Write the text image to a file. --->
<cfimage action="write" source="#myImage#" destination="text.tiff" overwrite ="yes">

<!--- Use the text image as a watermark in the PDF document. --->
<cfpdf action="addwatermark" source="c:/book/1.pdf" image="text.tiff"
    destination="watermarked.pdf" overwrite="yes">

For more information on ColdFusion images, see Creating and Manipulating ColdFusion Images. For an example of using DDX elements to create a text-string watermark, see Adding text-string watermarks.