Add documentation for all PDF tools

docs/tools/adjust-colors.md

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+---
+title: Adjust Colors
+description: Fine-tune brightness, contrast, saturation, hue, temperature, tint, gamma, and sepia in your PDF.
+---
+
+# Adjust Colors
+
+A full color grading toolkit for PDFs. Adjust eight independent parameters -- brightness, contrast, saturation, hue shift, temperature, tint, gamma, and sepia -- with a live preview that updates as you move each slider.
+
+## How It Works
+
+1. Upload your PDF file.
+2. The editor opens showing a preview of the first page and a color settings panel.
+3. Move the sliders to adjust each color parameter. The preview updates in real time.
+4. Click **Reset** to restore all sliders to their default positions.
+5. Click **Apply** to process all pages and download the adjusted PDF.
+
+## Options
+
+- **Brightness** -- Lighten or darken the entire page (-100 to +100).
+- **Contrast** -- Increase or decrease the difference between light and dark areas (-100 to +100).
+- **Saturation** -- Boost or reduce color intensity (-100 to +100). Setting to -100 produces a grayscale result.
+- **Hue Shift** -- Rotate the color wheel to shift all colors uniformly.
+- **Temperature** -- Shift colors warmer (yellow/orange) or cooler (blue).
+- **Tint** -- Add a green or magenta cast.
+- **Gamma** -- Adjust midtone brightness using a gamma curve. Values below 1.0 darken midtones; values above 1.0 lighten them.
+- **Sepia** -- Apply a classic sepia tone effect. Higher values produce a stronger brown tint.
+
+## Features
+
+- Eight independently adjustable color parameters
+- Live preview that responds immediately to slider changes
+- Reset button to quickly return to defaults
+- Processes all pages in the document
+- Works with any PDF content (text, images, graphics)
+
+## Use Cases
+
+- Brightening a dark scan or correcting overexposed pages
+- Desaturating a colorful document to reduce ink usage before printing
+- Applying a sepia tone to create an antique look for certificates or awards
+- Correcting color temperature on photos embedded in a PDF
+- Boosting contrast on faded or low-quality scanned documents
+
+## Tips
+
+- For a quick grayscale conversion, drag the saturation slider all the way to -100.
+- The gamma slider is particularly useful for improving readability of scanned documents where midtones are too dark or too light.
+- Like the other image-effect tools, this rasterizes each page. The output will be image-based, so text will not be selectable.
+
+## Related Tools
+
+- [Invert Colors](./invert-colors)
+- [Scanner Effect](./scanner-effect)
+- [Background Color](./background-color)