I have some pdf files I downloaded from the Internet that seem to have a lot of hidden text that I cannot see or read but the find function lists words I search for. I have current version of the fee acrobat reader but do I need another tool to see the hidden text? I tried changing background and foreground colors to white and black but that did not help. I read that pdf files can hide text using layers but no idea what that is all about.
I would try using Select All (under Edit, or Ctrl+A), then copying the text and pasting it into some other app such as Wordpad where you can change the font and read the text.
Alternatively, if you don't mind using a different app, you can download Foxit Reader (made by the company I work for) and use the "Text Viewer" button. This should show all text on a page in plaintext format. The button is available here in the "View" tab:
Unfortunately I don't believe Adobe Reader has the same functionality.
I found that Adobe Illustrator can do this by changing the colors to high contrast. This did not work in Acrobat Reader for some reason.