Delta Container Protocol (DCP)

Immutable PDF Editing via Deterministic Overlay

The Delta Container Protocol (DCP) establishes an innovative approach for modifying PDF documents without altering their internal structure. This open protocol allows users to edit PDFs non-destructively, treating them as immutable visual substrates while applying a deterministic overlay described by a delta ledger.

Core Concept

Rather than performing invasive edits on complex PDF structures, DCP employs a straightforward method:

Original PDF (immutable)
        +
Delta Recipe (JSON)
        →
Rendered Result (flattened image)

By ensuring that the original file remains unchanged, DCP provides stability and reversibility in document transformations.

Key Features

Versatile PDF Processing

DCP accommodates a wide range of PDFs, including:

• Scanned PDFs
• PDFs generated from Word or LibreOffice
• PDFs featuring embedded fonts
• Read-only PDFs (with no password)

Since DCP operates purely on rendered pixels, compatibility is broad and inclusive.

Deterministic Visual Replacement

With DCP, users can:

• Erase rectangular regions
• Insert text
• Control position, size, baseline, and color of elements

This guarantees that identical inputs will yield identical outputs, providing consistency.

Round-Trip Reproducibility

Each DCP container allows for the extraction of:

• original.pdf
• delta.json

This makes it possible to regenerate the exact same visual result consistently.

Auditability

DCP maintains a comprehensive record of all changes in a human-readable JSON format. This transparency enables users to inspect modifications, including their locations and sequence.

Corruption Resistance

DCP's methodology ensures that the internal structures of PDFs, including their object trees, fonts, streams, and cross-reference tables, are never altered. Consequently, the risk of PDF corruption is eliminated.

Limitations of DCP

DCP intentionally avoids certain functionalities, and these should be noted:

• No Internal PDF Text Editing: Any inserted text is represented as pixels, so standard functions like Copy/Paste and Search are not possible.
• No Semantic Understanding: DCP does not recognize document structures like paragraphs or columns; it only processes rectangular areas.
• No Text Reflow: Overflowing text will not be adjusted automatically.
• No PDF/A Compliance Validation: While DCP creates standard PDFs with embedded files, they are not validated as strictly compliant with PDF/A standards.
• No Automatic Page Creation: New pages will not be created by DCP.

Design Philosophy

DCP embodies a philosophy rooted in fundamental principles:

• Immutability over mutation
• Composition over modification
• Determinism over heuristics
• Transparency over hidden logic

Practical Applications

DCP is particularly suited for:

• Forms
• Certificates
• Contracts
• Administrative documents
• Archival corrections

However, it is not designed for use with books, magazines, or documents requiring complex typography and flowing multi-column layouts.

Conclusion

DCP redefines the interaction with PDF documents. By accepting the limitations inherent in the PDF format and providing a clear, reproducible method of applying changes, DCP stands out as a modern solution for document editing.