How to Watermark and Stamp a PDF File for Free?

(For the latest PDF files Merger Software please have a look at the top of the left margine, inside the red box.) Now this first version of software for watermarking, stamping pdf files with text and image is ready. User can change font size of the text and decides for the font and style. They also can  decide for the position and the angle that text appears on the page. Some PDF creators such as the scanners create PDF's which are completely opaque. In such PDF's watermarks go under the PDF box becomes hidden and unseen. In such cases my software allows users to put the watermark on the top of the pdf over the box. If the watermark obscures part of the texts then you can reduce the opacity of the watermark to become transparent enough to make the underlying text visible for reading. Then looks as if it is under the text. You can reduce opacity to zero to create a hidden watermark later can be recognized by you. If you use a hidden watermark "web URL" on your PDF, at its position a link becomes created that shows itself with the small "clicking" hand.cursor. In this way you can make your document active. User can change direction of the stamp or the watermark text between 90 degrees clockwise (-90) and 90 degrees counter-clockwise (+90), perhaps to be used for the landscape pages. The position where you put the watermartk is selected visually on the "measurement board" by a "double-click" on the "Get Mouse" button. Measurement board shows relative places of your document. Precise coordinates in terms of the size of the page of your document are shown in the X and Y text boxes at the bottom of the GUI. If you "double-click" on the cross hair point, those coordinates will be registered for the watermarked document. Then press on the OK button to have your stamped document. The resulting document comes with a filename that does not exist in the directory hence, your original remains as before untouched.
You can select to use an image for the watermarking. If you decide to put the image as the over layer on your pdf document there is an option in this software such that you can change its opacity to make it transparent and to be able to see contents underneath of the page. You also can choose to blow up your image in terms of the percentage, by adjusting knob. Enjoy!
Please go here
18/March/11: Now with a Visual Help page here.
Update, November 2014 : Dysprosium (Dolce edition) has been released based on iText from mid of April 2014 and smoothly on a nightly basis added more features and now I have deprecated many scattered pieces of PDF utilities I already released. There are so many features that I cannot write complete instructions for all of them. From other previous pieces only Signature manager has been remained to be integrated. I sorted out PDF viewer problem somehow satisfactorily.)