The following is a Plus Edition article, written by and copyright by Dick Eastman.If you have saved a bunch of PDF documents, ranging from single pages of information to entire genealogy books published many years ago, you may have noticed that some of them are searchable while others are not.
When a document is scanned and converted into a PDF file, the resultant file is simply a picture of the original pages. As with any picture, the person viewing the image cannot search for text inside the images. That's true of pictures taken with your digital camera, and it is also true for PDF images. As far as your PDF viewer is concerned, the document doesn't contain any text to edit or search—just one huge graphic.
Some years ago Adobe added an optional capability in its popular PDF creation software. After the creation of the original image, "special processing" could embed searchable text into the PDF file. The ability to add searchable text is optional; the person who creates the PDF file may elect to add searchable text or not. However, not all PDF files are searchable, even today.