We will generate an HTML file that perfectly displays your PDF on any mobile device.Supports MP3, WAV, OGG, M4A, FLAC, and more.
✅ Secret PDF Generated!
📁 HTML: Opens in any browser — audio plays automatically
// How to use this tool
1
Upload: Choose a PDF document and an Audio file. Click "Generate Secret PDF".
2
Download HTML: You will receive a self-contained HTML file. This file contains both your PDF and the audio.
3
Share: Send the HTML file via WhatsApp, Telegram, or Email. When the receiver opens it, they will see a "Tap to view Document" prompt. Upon tapping, the PDF will be displayed natively, and the hidden audio will play automatically!
// About This Tool
What is Secret PDF?
Secret PDF is a free online steganography tool that lets you hide audio files inside PNG images. It uses Least Significant Bit (LSB) encoding to embed audio data invisibly into the pixel color values of an image. The visual appearance of the image remains unchanged to the human eye, but the audio can be perfectly extracted later. All processing happens 100% in your browser — your files are never uploaded to any server.
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100% Private
All processing runs entirely in your browser. Your files are never uploaded to any server.
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Any Audio Format
Supports MP3, WAV, OGG, M4A, FLAC and any other audio format your browser can handle.
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Always Free
The Secret PDF tool is completely free with no sign-up, no subscription, and no limits.
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Truly Invisible
LSB steganography changes only the least significant bit of each color channel — completely invisible to the eye.
// FAQ
Frequently Asked Questions
Audio steganography hides audio data in the least significant bits (LSBs) of an image's pixel color values. Each pixel has RGB channels with 8-bit values (0-255). Changing the last bit changes the value by at most 1, which is invisible to the human eye but allows us to encode binary data.
The output must be saved as PNG. JPEG and WebP use lossy compression that alters pixel values, destroying the hidden data. Never re-compress, screenshot, or send the image through apps that re-encode images (WhatsApp, Instagram, etc.).
The capacity depends on image resolution. Each pixel stores 3 bits (one per RGB channel), so a 1920×1080 image can hold about 760 KB. Use higher resolution images for longer audio clips.