Use OCR software that supports PDF input
Open the PDF in the OCR tool
Select the pages or document to process
Choose the output language
Run OCR on the PDF
Save or export the OCRed PDF
Verify the text layer by searching within the PDF
Use Adobe Acrobat Pro: Tools > Scan & OCR > Recognize Text
Use ABBYY FineReader: Open PDF > OCR > Save as searchable PDF
Use Tesseract with OCRmyPDF for command-line OCR
Use Google Drive: Upload PDF > Open with Google Docs > Download as PDF
Use online OCR services if the document is not sensitive
Check scan quality before OCR for better accuracy
Rotate, deskew, or clean the scan if needed before OCR