Technical7 min read2026-02-22
How PDF Compression Actually Works Behind the Scenes
A deep dive into Flate algorithms, image downsampling matrices, and font subset optimization.
By Pdfyara Editorial Team
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The Internal Structure of a PDF
A PDF is structured as a directed graph of objects: dictionaries, arrays, streams, strings, and numbers. When optimizing a PDF, the compressor analyzes which objects contribute the most bytes to the total file size.
Lossless vs Lossy Optimization
Lossless optimization strips unreferenced object streams, cleans duplicate font descriptors, and applies optimal Deflate compression. Lossy optimization re-samples high-DPI photographs to screen-friendly resolutions.
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