To get the highest possible recognition rate, make sure you select the desired language within the list provided when selecting the OCR Engine box and also set the Resolution at 300 DPI or higher. For example, if the PDF you want to recognize includes French, you should choose French as your OCR engine language.
Tips: Scanning at 300 DPI produces the best text for conversion. At 150 DPI, OCR accuracy is slightly lower. At 600 dpi, both scanning and processing are slower than it is at 300 DPI.