How does SaferPDF work?

Understanding PDF Compression and How It Works

PDF compression is a process that reduces the size of PDF files, making them easier to manage and share. This is particularly useful for large documents that contain high-resolution images or extensive data.

Compression works by eliminating redundant data and using more efficient encoding methods for the content of the PDF. There are two main types of compression techniques: lossless and lossy. Lossless compression reduces the file size without losing any quality, which means the original PDF can be perfectly reconstructed from the compressed file. Lossy compression, on the other hand, reduces file size by permanently eliminating certain data, which can slightly affect the quality of images and text in the document depending on the level of compression applied.

Exploring Ghostscript: The Standard in PDF Compression

Ghostscript, created in the late 1980s by L. Peter Deutsch, is an open-source interpreter for the PostScript language and for PDF files. It has become a recognized standard for processing these file types, extensively used for viewing, converting, and compressing PDF files. Through Ghostscript, we can re-encode text, images, and vector graphics, optimize embedded fonts, and remove unnecessary metadata or unused objects. Distributed under the Affero General Public License (AGPL), it ensures that all derived works also remain open source. For more detailed information about Ghostscript, you can visit the official site here .

Bringing Ghostscript to the Web: A Collaborative Effort with the Open Source Community

We, the SaferPDF team, in collaboration with the broader open source community, have taken on the ambitious challenge of porting Ghostscript to the web to enhance its accessibility and functionality. By utilizing Emscripten, we’ve successfully compiled Ghostscript’s C code into WebAssembly, allowing it to run at near-native speed within web browsers. WebAssembly offers a secure execution environment, which is crucial for handling sensitive documents online without risking data exposure because we do not exit the browser runtime. More tech here

To ensure that the intensive tasks of PDF compression do not interfere with the browser’s responsiveness, we employ WebWorkers for background processing. This technical choice is crucial for not blocking the main thread of the browser, thus maintaining a smooth and responsive user experience.

We chose to leverage this powerful tool in the browser primarily because of its robust capabilities and the inherent data safety it offers—no data leaves the browser, ensuring privacy and security. Although running Ghostscript in this new environment may be slightly slower than its native execution due to current limitations in parallel processing, the trade-off for enhanced security and data privacy is well worth it. Moreover, as we have modified Ghostscript, we are required to open source our changes, in line with the AGPL license. This transparency not only upholds our commitment to the open source ethos but also ensures that our community can continually improve and build upon our work. For a more in-depth look into our contributions and ongoing projects, feel free to visit the SaferPDF GitHub repository here .