PDF Metadata Steganography Hider
Hide text or files in PDF metadata using 6 methods — XMP fields, custom Info keys, object streams, whitespace encoding, incremental updates, and file attachments. AES-256-GCM, batch HKDF watermarking, CTF mode.
Try the demo instantly
Loads a sample document — no upload needed
Drop a PDF file here or click to browse
PDF 1.4–2.0 · Max 50 MB
Processing happens entirely in your browser — nothing is uploaded.
How to Hide Data in a PDF (5 steps)
- Upload a PDF (1.4–2.0, up to 50 MB) — it's analysed instantly, right in your browser
- Choose a mode: Quick (one-click watermark), Standard (method picker + batch), or Forensic (all 6 methods + CTF tools)
- Type your secret message, a CTF flag, or upload a file to hide
- Pick a hiding method — XMP Metadata is the easiest, Whitespace Encoding is the stealthiest
- Add a password for AES-256-GCM encryption (recommended), then click Embed & Download
PDF Metadata Steganography — 6 Methods Compared
| Method | Technique | Capacity | Best For |
|---|---|---|---|
| XMP Metadata | PDF Info dictionary field (Author, Title, Subject, ...) | ~60 KB per field | Quick document watermarking, beginner CTF |
| Custom Metadata Key | Non-standard Info dictionary key (e.g. DocumentID) | ~60 KB | Professional watermarking, hidden attribution |
| Object Stream | Unreferenced (dereferenced) PDF object | Up to the 50 MB upload limit | Large payloads, advanced CTF challenges |
| Whitespace Encoding | Space (bit 0) / tab (bit 1) inside text-showing strings | 1 bit per word gap — depends on text content | Maximum stealth, expert CTF (SNOW-style) |
| Incremental Update | PDF's own incremental-update append mechanism | Up to the 50 MB upload limit | Large files — original bytes stay untouched |
| Embedded File Attachment | PDF file attachment (/EmbeddedFile) | Up to the 50 MB upload limit | File smuggling, beginner CTF |
Frequently Asked Questions
Is this for removing PDF metadata?
No — this ADDS hidden data to PDFs (steganography). For metadata removal, use a tool like PDF24 or PDFCandy. This tool is for watermarking, CTF challenges, and document tracking.
How much data can I hide?
Depends on the method: XMP Metadata and Custom Metadata Key cap around 60 KB (the classic PDF string-length limit); Object Stream, Incremental Update, and Embedded File Attachment scale up to the 50 MB upload limit; Whitespace Encoding depends on how many word gaps your PDF's text actually has — often just tens to hundreds of bytes.
Will the PDF look different?
No visual changes for XMP, Custom Key, Object Stream, Incremental Update, or Embedded File — file size increases slightly (payload + AES-GCM overhead if encrypted). Whitespace Encoding replaces some spaces with tabs inside the underlying text objects, invisible to the rendered page but technically a byte-level change.
What tools can detect the hidden data?
XMP Metadata: ExifTool, pdf-parser (easy). Custom Metadata Key: pdf-parser with a targeted search (medium). Object Stream: manual PDF structure analysis (hard). Whitespace: a dedicated SNOW-style analyzer (very hard). Incremental Update: visible as file-size growth / multiple xref sections. Embedded File: ExifTool, pdf-parser, binwalk (easy).
Does this work on password-protected PDFs?
No — encrypted PDFs must be decrypted first. This tool embeds a SEPARATE, optional AES-256-GCM layer around your hidden payload (independent of the PDF's own document-encryption feature, which this tool doesn't touch).
What's Multi-Method Embedding?
A Forensic-mode feature that embeds the same payload into several methods at once (e.g. XMP + Custom Key + Object Stream) — a CTF challenge survives a solver missing one location, or a PDF re-save that strips one substrate but not the others.
Is this legal?
Yes, for legitimate uses (watermarking, CTF, research). It becomes illegal only if used to hide illegal content, evade law enforcement, or violate a service's terms of use.
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