Mark a text in Acrobat Reader

Hi everyone

I have a problem with the textmarker in Acrobat Reader. Every time I want to highlight a text passage I have to click on the marker button. In the beginnging, when I just had downloaded the app, I could just click on the button once and use the marker all over the text. Now I need to click on the marking tool every time I want to highlight something. It is a little annoying to me as it takes me so much more time than usual while I read a text. 

Does anyone have an idea how I could change this?

Best regards