Adobe Acrobat Output Preview show white text

Hello. There is a way to do this as I found it years ago but since have formatted my computer and lost the settings. So I know it;s possible. 

When opening a PDF in Adode Acrobat, opening Output Preview. In the show drop down box you have the option to view TEXT and it will show you all non outlined text in your document. This works really well if you have black or coloured text but you're unable to see white text as it's the same colour as the background. 

Using 'Set page colour' and selecting a 50% grey will not work as it then makes the text 50% gret too. 

I recal something about page transparency. So when viewing a PDF which has white text on a colour background, then selecting to show TEXT, you can see the text and know it't not outlined. 

Thanks, Nick