This paper deals with the development and assessment of a watermarking technique which is suitable for scanned PDF documents. The watermark will serve two purposes. The first one is a logo to protect the copyright ownership. This watermark should be invisible and secure and can be extracted even if the document has gone through slight image manipulations. The second watermark will be used to authenticate the document. A slight editing in the document will change the second watermark and indicate forgery. The algorithm was tested successfully on a variety of scanned documents and the performances of the algorithm were assessed.