OCR: What It Is and When It Works
A scan is just a picture of a page
Your scanned page looks like a document, but to a computer it is a photograph. There is no text underneath. OCR works by looking at the shapes on the page and matching them to letters.
What makes OCR work well or fail
A flat, well-lit, high-contrast scan of a standard printed font gives OCR its best chance. A photo taken at an angle, with shadows, low resolution, or unusual fonts makes the problem harder.
OCR vs PDF to Text: Which to use
PDF to Text: when the document has a text layer. OCR: when the document is a scan or photo with no selectable text. If you can highlight text in your PDF viewer, you do not need OCR.
If OCR accuracy looks poor, check the scan quality first. A slightly higher-resolution scan, taken straight-on, fixes more errors than anything on the processing side.