Watermarking has proved its great reliability and flexibility for property rights protection and tamper detection of diverse forms of online distributed data. Among the different mediums in which watermarking technology is used, text watermarking represents the most challenging issue due to the distinctive nature of its various formats. Plain text is widely used for transferring information on the internet. Despite this, there is a lack of used plain text watermarking techniques, so obviously it's necessary to focus on that point and pay it more attention. In this paper a blind text watermarking approach is proposed for copyright protection and tamper detection of plain text by inter-word spacing (depending on a secret binary number and a key word) and text fingerprint through using MD5 hash function. Simulation results proved the success of our approach in detecting any tiny content tampering and due to the secret key and the fingerprint of watermarked text copyright protection are accomplished efficiently. This approach is a combination of several steps which work cooperatively to reach the desired goals.