How to highlight a text in pdf opened in web browser

When pdf file is opened in browser, extensions like Diggo cannot highlight the text in the pdf.

Are there any extensions or ways in which this can be achieved?

Or opening a pdf using a application like adobe acrobat is the only option.

I use an application called FOX IT PDF(LINK), it's free and if you define it to open the pdf inside browser it allows you to highlight the text you want

The pdf.js project provides a means to display PDF in the browser without the need of plugins - this allows browser's search to work and it should also play well together with extensions like Diggo. You can install the Firefox extension, starting with Firefox 14 this extension will be built into the browser. The Chrome extension is experimental, they currently don't seem to provide pre-built packages.

It has been two years since the question was asked, but I found an extension that works well with Google Chrome called Kami. It allows to highlight a PDF within the Chrome browser, just drag and drop.