This grays out the textarea altogether and inhibits any change in the text as well as text highlighting.If you want to create disable text area use the code below.

<textarea cols="50" rows="5" disabled="yes">TYPE-YOUR-TEXT-HERE</textarea>

Look at the example below.

Code:

<textarea cols="50" rows="5" disabled="yes">Pagerank is how Google as number one search engine that most of internet users use to find anything on internet give a rank to your site. It gives ranking based on your quality backlink. So to increase pagerank of your site, you need to get as much as possible quality backlinks to your site. Quality backlink meant here is backlink from a site which its content is relevant with your content</textarea>

Result:
Pagerank is how Google as number one search engine that most of internet users use to find anything on internet give a rank to your site. It gives ranking based on your quality backlink. So to increase pagerank of your site, you need to get as much as possible quality backlinks to your site. Quality backlink meant here is backlink from a site which its content is relevant with your content