How to improve OCR accuracy for scanned PDFs

Start with a readable source

For ordinary printed text, a clean scan around 300 DPI is a strong baseline. Very low resolution removes character detail, while extremely high resolution increases processing time without guaranteeing better recognition.

Avoid aggressive image compression. Block artefacts around small letters can turn punctuation into noise and make similar characters harder to separate.

• Prefer a flatbed or document scanner for important records
• Keep pages straight and fully inside the frame
• Use even lighting for phone captures
• Avoid screenshots of already compressed previews

Fix rotation, shadows, and background noise

Automatic page rotation helps with pages turned by 90 degrees, but small skew and perspective distortion still affect line detection. Rescanning is often faster than trying to repair a severely angled image.

Receipts and coloured forms can have weak contrast. A clean grayscale scan may recognise better than a dark colour photo, especially when text sits on a patterned background.

Language and document structure matter

Recognition works best when the OCR engine has the correct language data. Mixed-language documents, uncommon names, serial numbers, and technical abbreviations need closer review because dictionaries provide less help.

Tables, multiple columns, handwritten notes, stamps, and text over images complicate reading order. Searchable PDF can still be a good output because it preserves the visible page even when copied text is imperfect.

Review the fields that carry risk

Do not review every word with equal effort. Focus on values that can change a decision: invoice totals, dates, account numbers, legal names, addresses, and reference identifiers.

Keep a visual copy beside extracted text during review. If a result will feed accounting, legal, or identity workflows, use human verification before automation continues.

• Compare totals digit by digit
• Check decimal and thousands separators
• Review names with accented characters
• Confirm page count and missing pages