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PDF documents present their pages as images. They can be marked-up and
commented, but the ability to change the basic text is limited. Most PDF
files can be searched, because the file has two layers. There is an image layer
that is presented on-screen. Behind that there is usually a text layer that can
be matched to the characters displayed on the screen.
When the starting point for a PDF file is a set of images, or a scanning
process, this text layer is not present and the result is an image-only PDF.
When the starting point is an editable document, the text layer can be
created and the PDF is called 'Normal' or 'Searchable'. The creator of a
PDF can require provision of a password to allow access the text layer.
How does PDF Converter work?
PDF Converter has the ability to perform Optical Character Recognition
(OCR). This is the process of extracting text from an image. It does not
need to use OCR to unlock PDF files with an accessible text layer - it must
capture the page layout and arrange the given text and other elements
correctly on each page in the new document.
Display layer
Text layer