Not sure what you mean by "clickable". If you mean can you select, and then copy text in pages...then yes, it's built-in. Just press and hold on the text, then a pair of bookends will appear and the word between will be highlighted. You can move the bookends to capture more or less text. Alternatively you can click on the box at the top that has 4 squares in it (or the words SELECT ALL - depending on your version/phone), and it will select ALL text. Once you've selected what you want, you can click on the other boxes above to cut (scissors) or copy (two papers stacked). You can also email, share in text, etc.
If you mean somehow making plain text in a webpage into a hyperlink to take you to a search, for instance, you can use the method above and Paste it into the address bar of the browser, or into a Google search window.
If that's not what you're looking for, then I'm lost.
OK, so I was on the right track. Here's possibly the issue. Not ALL you see on a text page in websites is ACTUALLY text. Many web designers opt to use PDF documents or JPG images to display text. The reasons are varied, but one obvious reason is that copying and appropriating their text content is more difficult. It's also impossible for the search engine spiders to "spider" the text in those images, so where they may gain a certain level of copyright protection, they miss out on HUGE results in the search engines.