OFD (Open Fixed-layout Document) is China's national standard fixed-layout document format, which has been rapidly adopted in recent years in government documents, electronic certificates, bidding documents, and other fields. Many people find OFD unfamiliar when they first encounter it—it looks much like PDF, but the two are entirely different technical systems. This article systematically compares the differences between OFD and PDF and introduces methods for compressing OFD files.
If you are not yet familiar with the overall logic of file compression, we recommend first reading our Complete File Compression Guide to understand the basic principles of compression before returning to this article.
1. What Is OFD: The National Standard Fixed-Layout Document
OFD (Open Fixed-layout Document) is a fixed-layout document format standard published by the Standardization Administration of China, with the standard number GB/T 33190-2016. Unlike PDF, which was developed by Adobe and later became an ISO international standard, OFD is a Chinese national standard for fixed-layout documents, aimed at addressing the need for self-controlled, domestically developed technology in the fixed-layout document domain.
OFD files use XML to describe document structure and are organized as ZIP packages, essentially serving as a compressed container containing multiple XML files and media resources. It supports text, images, graphics, signatures, seals, animations, and other layout elements, and can precisely preserve document layout to ensure consistent rendering across different devices.
Since 2020, OFD has been widely adopted in the electronic document systems of party and government agencies, gradually becoming the de facto standard for fixed-layout documents in the government sector. Today, OFD files are increasingly common in scenarios such as electronic invoices, electronic certificates, and electronic contracts.
2. Core Differences Between OFD and PDF
Although OFD and PDF are both fixed-layout document formats with similar functional positioning, they differ significantly in their technical systems and ecosystems:
| Dimension | OFD | |
|---|---|---|
| Format Standard | Chinese national standard GB/T 33190-2016 | ISO 32000 international standard (originated from Adobe) |
| File Structure | XML + ZIP container, open structure | Binary/text hybrid, relatively closed structure |
| Use Scenarios | Government documents, electronic certificates, bidding | General documents, contracts, reports, publications |
| Supporting Tools | Limited, primarily domestic tools such as Shuke and Foxit | Mature ecosystem, Adobe, Foxit, and many free tools |
| Signature Support | Native electronic signature support, compliant with national cryptography standards | Supports digital signatures, national crypto support requires additional adaptation |
| International Recognition | Primarily domestic application | Universally used worldwide |
2.1 Format Standard
OFD is a Chinese national standard with publicly transparent technical specifications and document structure based on XML, facilitating domestic adaptation and integration of national cryptographic algorithms. PDF is an international standard with the most mature ecosystem and global acceptance, but it raises self-control considerations in classified and government scenarios.
2.2 Use Scenarios
OFD is primarily applied in domestic official scenarios such as government documents, electronic certificates, electronic invoices, and bidding; PDF covers virtually all general document scenarios, from business contracts to academic papers, from e-books to publications, with a broader scope of application.
2.3 File Structure
OFD files are essentially ZIP packages, using XML internally to describe pages, text, images, and other elements, with a clear and easily parsable structure. PDF uses a binary and text hybrid format with a relatively complex internal structure that appears more like a "black box" to ordinary users.
2.4 Supporting Tools
PDF's tool ecosystem is extremely rich, ranging from free built-in browser viewers to professional Adobe Acrobat, with all kinds of editing, conversion, and compression tools available. In contrast, OFD's toolchain is still in its early stages of development, with limited software capable of viewing and editing OFD, and tools supporting OFD compression being particularly scarce.
3. OFD in Government Documents
The promotion of OFD in the government sector has practical background. Traditional government documents were primarily paper-based, and the electronic transition required a fixed-layout format that could precisely preserve layout, support electronic signatures, and comply with national cryptographic management requirements. While PDF is functionally powerful, as a foreign standard, it raises self-control concerns for use in classified information systems.
As a national standard, OFD natively supports electronic signatures and seal verification compliant with national cryptographic standards, meeting the requirements for authenticity, integrity, and non-repudiation in document circulation. Currently, electronic document systems of party and government agencies across the country have adopted OFD as the standard format, and electronic licenses such as electronic business licenses and real estate registration certificates are gradually migrating to the OFD format.
As the scale of application has grown, OFD file size issues have emerged—large numbers of embedded scanned documents and high-resolution seal images cause government documents to routinely reach tens of MB, creating pressure on storage and transmission, and driving the need for OFD compression.
4. OFD Compression Methods
The principles of OFD compression are highly similar to PDF compression, with the core being optimizing the parts that occupy the most space within the file. Specific methods include:
- Image resampling: Scanned documents and seal images in OFD files are typically the largest contributors. Reducing high-resolution images to reasonable resolution (e.g., 300dpi to 150dpi) can significantly reduce file size.
- Font subsetting: Keeping only the character glyphs actually used in the document and discarding unused font data, which is particularly effective for Chinese documents.
- Cleaning up redundant objects: Removing unreferenced resources and duplicate objects within the OFD package to streamline the document structure.
- Image format optimization: Converting uncompressed bitmaps to compressed formats like JPEG to reduce image resource usage.
Since OFD is itself a ZIP container, the file structure already undergoes one layer of compression. Therefore, the key to OFD compression lies in optimizing internal resources (images, fonts) rather than simply adding another layer of archive compression. This is consistent with the approach to PDF compression—for detailed PDF compression methods, see PDF Compression Principles & Methods.
A 50MB OFD scanned government document, after proper image resampling and font subsetting, can typically be compressed to 8-12MB, with text and seals still clearly legible, fully meeting government circulation and archiving requirements.
5. The Scarcity of OFD Tools
Although OFD's status as a national standard is clear, its tool ecosystem is far less mature than PDF's. Currently, software that can view OFD is primarily limited to domestic tools such as the Shuke reader and Foxit OFD, and tools capable of compressing OFD are even more scarce. Many users who receive a government OFD document of tens of MB find no suitable tool to compress it and can only store or transmit it as-is.
Recognizing this gap, SmartSlim was among the first to include OFD as a supported format, providing a compression experience consistent with PDF. Users can complete OFD compression locally, with files never leaving the device, solving the size problem while meeting government data security requirements. For the compliance differences between local and online compression, see Enterprise File Processing Compliance Guide Under the Data Security Law.
6. Frequently Asked Questions (FAQ)
Can OFD files be converted to PDF?
Yes. Some OFD readers and conversion tools support exporting OFD to PDF. However, note that OFD-specific information such as electronic signatures may not be fully preserved during conversion. We recommend exercising caution when converting for long-term archiving or legal validity scenarios, and making backups before conversion.
Does OFD compression affect the validity of electronic signatures?
Proper OFD compression only optimizes resources such as images and fonts, and does not modify signature data or document hash verification information, so it does not affect the validity of electronic signatures. We recommend using professional tools and verifying the signature status after compression to ensure the legal validity of government documents is not affected.
Do I need to use OFD for regular office work?
For general business documents, PDF is sufficient. OFD is primarily used for official scenarios such as government documents and electronic certificates. If you do not work with government agencies, there is no need to specifically use the OFD format. However, if you need to exchange electronic documents with government agencies, you may need to use OFD.
Conclusion
Although OFD and PDF are both fixed-layout document formats, they represent different technical approaches and application ecosystems. OFD, as a national standard, has a firm position in the government document domain; PDF, as an international standard, is irreplaceable in general office scenarios. The two are highly similar in compression methods—the core is optimizing embedded images and font resources. Faced with the scarcity of OFD tools, choosing a professional tool that supports OFD compression can make government document processing more efficient.
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