I've a scanned PDF and i can't seem to highlight the text of course using the preview on my OS X, is there a software that do that like in windows?
Ask Different is a question and answer site for power users of Apple hardware and software. It only takes a minute to sign up.Sign up to join this community
Highlighting text in a PDF assumes that there is text in the PDF to begin with.
When you scan a document to PDF, it is simply an image. You should still be able to use the annotation tools available in preview to draw on it and add notes, but you will not be able to highlight or copy text from it because there literally is no text in the document.
There is, however, a type of software called OCR, for Optical Character Recognition, that can be used to programmatically "read" the letters in the image of your document and write out accurate text to the PDF. Some of this software is pretty good, but it is rarely free. Some scanners come with OCR software, and the you may be able to find some software online that will let you try it out for free.
Running an image PDF through OCR software will provide it with text data that you can then highlight using the annotation tools in preview.
You can use ABBYY FineReader to recognise the text in the scanned PDF:
Create searchable PDFs ready for archiving
With a few mouse clicks you can turn paper documents into truly searchable compressed PDF files for archiving. Information in such archives can be easily retrieved at any time you need it by using keyword search, while document compression reduces the amount of disk space used. You can also save files to a PDF/A format for long-term archiving.