This paper provides a new secured, invisible approach to watermark text documents. For integrity verification of text documents, the watermark has to depend on a secret key and on the original document. It is important that the dependence on the key should be sensitive. In this paper, a novel watermarking technique is proposed for content authentication and integrity of text documents. The proposed method makes use of the concept of eigen values by constructing a Line-Document matrix for the whole text document to be watermarked. These eigen values are used to form a secret key for generating the watermark. Embedding is done in the bit plane of the document image which will be imperceptible. Comparison of embedded and extracted secret keys detects any small alterations done to the document. This technique is fragile and hence tamper detection is high. © 2009 ESRGroups France.