Add documentation for all PDF tools

docs/tools/scanner-effect.md

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+---
+title: Scanner Effect
+description: Make your PDF look like a scanned document with adjustable noise, rotation, blur, and paper aging effects.
+---
+
+# Scanner Effect
+
+Transform a clean digital PDF into something that looks like it came out of a flatbed scanner. The tool applies configurable noise, slight rotation, blur, brightness shifts, and optional yellowing to simulate the imperfections of a physical scan.
+
+## How It Works
+
+1. Upload your PDF file.
+2. The editor opens with a live preview of the first page alongside a settings panel.
+3. Adjust the scan effect parameters using the sliders and toggles.
+4. The preview updates in real time as you change settings.
+5. Click **Apply** to process all pages and download the result.
+
+## Options
+
+- **Colorspace (Grayscale toggle)** -- Convert the output to grayscale for a classic black-and-white scan look.
+- **Border** -- Add a subtle dark border around the page edges to mimic scanner border artifacts.
+- **Rotate** -- Apply a slight rotation (-5 to +5 degrees) to simulate misaligned paper feeding.
+- **Rotate Variance** -- Add random variation to the rotation angle so each page tilts slightly differently.
+- **Brightness** -- Shift the overall brightness up or down.
+- **Contrast** -- Adjust contrast to simulate toner quality variations.
+- **Blur** -- Apply Gaussian blur to soften text edges like a low-quality scan.
+- **Noise** -- Add random pixel noise to simulate scanner sensor grain. Higher values produce grainier results.
+- **Yellowish** -- Add a warm yellow tint to simulate aged or recycled paper.
+- **Resolution** -- Set the output DPI. Lower values create a more pixelated, scan-like appearance.
+- **Reset** -- Restore all settings to their defaults.
+
+## Features
+
+- Real-time preview that updates as you tweak each parameter
+- Per-page random rotation variance for realistic variation
+- Ten independently adjustable parameters
+- Grayscale mode for authentic black-and-white scan output
+- Resolution control from low-DPI fax quality to high-DPI archive quality
+
+## Use Cases
+
+- Making digitally created documents appear to have been scanned and printed
+- Simulating physical document aging for historical document recreation
+- Testing OCR software against degraded scan quality
+- Producing documents that match the visual style of existing scanned archives
+
+## Tips
+
+- Start with subtle values. A noise level of 10-20, a slight 0.5-degree rotation, and minimal blur already produce a convincing scan look.
+- Combine grayscale mode with slight yellowing for a "photocopy of a photocopy" effect.
+- Lower resolution settings (100-150 DPI) create the most realistic fax-machine appearance.
+
+## Related Tools
+
+- [Invert Colors](./invert-colors)
+- [Adjust Colors](./adjust-colors)
+- [Background Color](./background-color)