my pdf text is too blurry. so i want to convert it to computer font from scanned image.i already tried increassing quality by adobe/edit/preferences/page display.
The problem is that the original image of the text is "in front" of the actual digital text of the PDF.
PDF is composed of overlapping visible and invisible layers. OCR attempts to use algorithms to identify text placement and size, then place text objects under the original images of the pages.
See these blog entries: blogs.acrobat.com
Also, please see question by @tel here for additional discussion:
How to replaces images of text in PDFs with formatted text using OCR
Without a professional subscription, I would use Adobe Acrobat DC to output as XML or DOCX, go into the XML and remove the images (e.g., using a regular expression), then try to apply text correction to the resulting document.
By the way, ABBYY FineReader has an option to save your OCR results as pure text — not invisible text under an image of the text. The software isn't cheap, but the investment can make sense if you're often doing OCR.