PDF files can contain lengthy documents. Using the highlight feature in Adobe Reader 9 helps organise notes and makes it easier to find important information. Adobe Reader 9 is a free PDF viewing program. Users can highlight, cross out or underline sections of any PDF document that allows comments. According to Adobe, Adobe Reader 9 is cross-platform with downloads available for Windows, Mac, Linux, Solaris and mobile devices. Adobe first released Reader 9 in 2008.
Open a PDF file in Adobe Reader 9.
Select "Document" in the top menu bar and choose "Security" and "Show Security Properties" from the drop-down menu.
Read the "Document Restrictions Summary." It will say "Commenting: Allowed" if the document settings allow you to highlight and comment on the PDF file. If it says "Commenting: Not Allowed," you cannot highlight and add comments to the PDF file. If it says "Content Copying: Allowed" you will be able to highlight a selection of text to copy and paste to another file.
Click on "Tools" in the top menu bar. Select "Comment & Markups" and the "Highlight Text" tool. The highlight text tool is a square button that has the letter "T" inside that has been highlighted in yellow. It also has a yellow highlighter in the top left of the button.
Click and drag the mouse pointer over the section of text you wish to highlight. To highlight larger areas, press "Ctrl" on the keyboard, click with a mouse and drag to highlight an entire rectangular area of text.
Save the PDF document so you can view your highlighting the next time you open the document.
If you are creating your own PDF documents that you would like to be commented on later, make sure you enable commenting. This can be done in Adobe Acrobat software by clicking "Comments" and then selecting "Enable For Commenting In Adobe Reader." Adobe has an online collaborative environment called Acrobat, which allows users to collaboratively create PDF documents. It offers free user accounts with limited uses. You can highlight text in any PDF document that has content copying allowed, even if comments are disabled. This highlighting will not save if you save the PDF document, but you can copy and paste selected text into another document.