KillerPDF

KillerPDF is a free, open-source PDF editor for Windows. View, annotate, OCR, merge, split, edit text, draw, sign, fill forms, print, flatten, and open password-protected PDFs without an Adobe subscription. Choose the compact Windows installer or the self-contained portable edition. Document processing stays on your computer, with no telemetry.

Full how-tos live on the help page (opens in a new tab); internals, formats, and limits on the technical page (opens in a new tab).

The KillerPDF.Engine

KillerPDF 1.8 introduces The KillerPDF.Engine, an independent and reusable .NET library for PDF 2.0, PDF/A, and PDF/UA document processing. It is a first-class area of this monorepo with its own public API, tests, corpus tooling, architecture documentation, [README](engine/README.md), and release history.

Features

• High-quality PDFium rendering with four view modes (Single, Continuous, Two-Page with a book layout option, Grid), tabbed documents, and a split pane for two documents side by side
• Annotate with inline text editing and font matching, word-wrapping text boxes, drawing, lines, highlights, images, and page-number or watermark stamps. Highlights use the Multiply blend so the text underneath stays readable, and every tab has its own undo and redo history.
• Built-in OCR (Tesseract bundled, no cloud): make searchable PDFs, OCR a page or region to the clipboard, extract all text; extra languages download on demand
• Organize pages: merge, split, insert, rotate, crop, extract, delete, drag-and-drop reordering; drop a folder or .zip onto the window to merge its contents
• Export one page or a multi-page selection as PNG or JPEG directly from the Pages panel
• Transform: rotate, scale, flip, deskew by drawing a level line, perspective correction for photographed pages, and a LEVELS section (black point, white point, midtones) for pale scans
• Forms: fill text, checkbox, radio, and comb fields as live controls and save back; digital signatures with a certificate from Windows or a .pfx file, plus drawn or imported signatures and initials
• Print with a real in-app preview, paper size and source selection, scale / position / margins / pages-per-sheet options at 300 DPI; Save Flattened rasterizes to a fully uneditable PDF
• Full-text search with highlighting, and column-aware text selection that copies multi-column pages in reading order
• Night-mode inversion works independently in each split pane. Thirteen themes, live accent colors, and toolbar styles provide 41 looks, while the resizable sidebar can dock on either side.