With the wide use of various communication technologies and Internet, it has become tremendously easy to reduce, communicate, and distribute digital contents. As far as there is authentication and copyright protection issue have arisen. Textual way of communication is the most widely used medium for traveling the data over the Internet besides images, audio and video. There are various platforms for the plain text such as books, newspaper, web pages, advertisement, research papers, legal documents, letters, novels, poetry, and many other documents. Security of text contents is a significant issue for copyright protection which can not be condoned. Here, zero watermarking algorithm based on occurrence frequency of vowels ASCII characters and articles for copyright protection of plain text is designed and implemented. Embedding algorithm makes use of frequency vowel characters and articles to generate a specialized author key. The extraction algorithm uses this key to extract watermark, hence identify the original copyright owner. Experimental results illustrates the effectiveness of the proposed algorithm on text documents encountering various tempering attacks.