Exis.PdfOcr 1.0.5

Exis.PdfOcr

Local, no-cloud OCR for PDFs — turns scanned (image) PDF pages into searchable PDFs by adding an invisible, selectable text layer over the page image. Built on Exis.PdfEditor, so the output round-trips through the same find/replace, redaction, and extraction APIs as any digital PDF.

Designed for workflows like HIPAA medical-document batch processing: 100% on-device, no network calls, and per-page OCR confidence is surfaced so you can flag low-confidence pages for human review.

Packages

Install all three for the batteries-included Windows experience:

dotnet add package Exis.PdfOcr
dotnet add package Exis.PdfOcr.Tesseract
dotnet add package Exis.PdfOcr.Windows

The core targets the same netstandard2.0;net8.0 surface as Exis.PdfEditor, so the same WPF (.NET), MAUI, and .NET Framework projects can consume it.

Usage

using Exis.PdfEditor;   // licensing
using Exis.PdfOcr;

// Exis.PdfOcr builds on the licensed Exis.PdfEditor — initialise it once at startup.
ExisLicense.Initialize();              // or ExisLicense.Initialize("XXXX-XXXX-XXXX-XXXX");

var result = await PdfOcr.MakeSearchableAsync(
    "input.pdf", "output.pdf", new OcrOptions { Languages = ["eng"] });

Console.WriteLine($"OCR'd {result.PagesProcessed}, skipped {result.PagesSkipped}, " +
                  $"avg confidence {result.AverageConfidence:P0}");

// Flag low-confidence pages for human review — confidence is never swallowed.
foreach (var page in result.Pages)
    if (page.WasOcrd && page.Confidence < 0.80)
        Console.WriteLine($"  Page {page.PageNumber} needs review (conf {page.Confidence:P0})");

• Digital and already-OCR'd pages pass through untouched — only true scans are rasterized and recognized, which protects quality and is fast on mixed documents.
• The output's text layer is invisible (PDF render mode 3) and positioned over the page image, so the page looks identical but text is now selectable and findable.

Progress reporting

var progress = new Progress<OcrProgress>(p =>
    Console.WriteLine($"[{p.Phase}] page {p.PageNumber}/{p.TotalPages}"));

await PdfOcr.MakeSearchableAsync("in.pdf", "out.pdf", new OcrOptions(), progress);

Languages

OcrOptions.Languages are Tesseract language codes ("eng", "spa", "vie", …). The Exis.PdfOcr.Tesseract package ships English (eng.traineddata). To add languages, drop the extra xxx.traineddata files into the package's tessdata folder (next to eng.traineddata in your app's output) and list them:

new OcrOptions { Languages = ["eng", "spa", "vie"] }

The invisible text layer embeds a Unicode font (DejaVu Sans), so accented and non-Latin names (e.g. Nguyễn, Peña) survive find/replace intact rather than being mangled.

MAUI / packaged apps

Where trained data isn't on disk as a plain file, ship it as a MauiAsset, extract it to a readable folder on first run, and point the provider at it:

var provider = new TesseractOcrProvider(tessdataPath: extractedTessdataDir);
await PdfOcr.MakeSearchableAsync("in.pdf", "out.pdf", new OcrOptions(), provider: provider);

Custom rasterizer / OCR engine

Both seams are pluggable. Implement IPdfRasterizer (e.g. a future Mac/Linux renderer) or IOcrProvider, and pass it to MakeSearchableAsync. If you omit them, the core discovers the Windows rasterizer and Tesseract provider by reflection — so the core itself never references Windows.* or the native OCR binaries.

Note on scanned-page de-identification

Replacing text in the OCR layer changes the selectable text, not the underlying scanned pixels: the visible image still shows the original characters. To remove a name from the visible scan as well, follow OCR with a pixel-redaction pass over the matched word boxes (Exis.PdfEditor's PdfRedactor). The OCR layer is what makes those words findable.