A note about searching scanned documents Scanned PDF files have two layers to them: a display layer, which is for on-screen viewing, and a hidden text layer, which is used for this search engine. When PDF files are created from scanned paper originals, Acrobat® tries to recognize the words so it can store them in the text layer. While the software is usually accurate, it is not perfect and some words are not read correctly. Equations, for example, often use unusual characters and symbols that are not recognized by Acrobat®. Occasionally, a few of these errors show up in the text layer and may affect your search results.