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Searchable PDF files keep the original scanned image for viewing, as well as OCR text in a hidden layer that can be used for Full-Text Searching the document or highlight text for copy and paste operations.
Full OCR conversions to PDF that don't include the original image will never preserve the original formatting 100%, especially if there are a lot of images or complex document layout.
Searchable PDF avoids this by keeping an image for viewing along with the text.
These are also known as Image+Text PDF files.