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Compress PDF
Compress PDF — Reduce File Size Online
Reduce your PDF file size by dropping unreferenced objects and deflating the streams that arrived uncompressed.
About Compress PDF
PDF files become unexpectedly large for three boring reasons: objects nothing points at any more, streams that were never compressed in the first place, and a cross-reference table written in the older plain-text form. This is especially common with PDFs produced by word processors, design tools, and scanning software that accumulate revision history and orphaned objects. This tool makes one pass at each. It walks the document outward from the entries in its trailer and deletes every indirect object that walk cannot reach; it deflates the streams that arrived with no compression filter at all; and it rewrites the file with its objects packed into compressed object streams and a cross-reference stream. Because the first pass keeps whatever is reachable, the document's own metadata such as title and author survives unchanged, and so do form fields and their values, bookmarks, page labels, named destinations, annotations and embedded attachments — they all hang off the catalog, so keeping them is not a special case, it is the definition of the pass. What this tool deliberately does not do is re-encode your images, downsample them, or subset fonts. The pixels and the text come out byte for byte identical, which is why a PDF that is mostly photographs barely moves while one carrying orphaned objects or raw streams can lose the large majority of its size. And if the rewrite would come out larger than the file you gave it — which is what happens to a PDF already packed this way — the download hands back your original bytes and the readout honestly says nothing was saved. Common uses include shrinking PDFs before email attachments, meeting upload size limits on web portals, reducing storage for document archives, and preparing files for faster download. The compression is lossless: the visual content, text, and layout are identical to the original.
Questions
How much smaller will my PDF get?
It depends entirely on what is inside the file. A PDF carrying objects nothing references any more, or content streams that were never compressed, can lose the large majority of its size. A PDF that has already been through this treatment loses nothing at all. The readout shows the before and after sizes, so you never have to guess which case you were in.
Does compression reduce image quality?
No. The work is structural only: unreferenced objects are dropped, streams that arrived uncompressed are deflated, and the objects are repacked into compressed object streams. Embedded images are never re-encoded or downsampled, so every pixel comes out identical to the one that went in.
Will compression work on scanned PDFs?
Scanned PDFs are mostly raster image data, already compressed by the scanner, so structural work makes only a small dent. For scans the highest-leverage move is reducing image resolution before the PDF is produced. This tool can still drop whatever the file no longer references on top of that, which on a scanner’s output is sometimes more than you would expect.
What happens if compression would make my file bigger?
You get your original bytes back. A PDF that is already garbage-collected, already deflated and already packed into object streams has nothing left to give, and rewriting it can come out the same size or a shade larger. The two files are compared and whichever is smaller is what you get — the readout then shows 0% saved and a note explains that the original won.
Why are there no quality settings?
There is nothing to trade. The whole operation is lossless — unreferenced objects dropped, uncompressed streams deflated, the structure repacked — and it starts the moment you drop the file. Because it never re-encodes your images or your text, a quality dial would have nothing to turn down.
Is my file uploaded to a server?
No. Transmute processes everything locally in your browser using JavaScript and WebAssembly. Your files never leave your device — there is no server, no upload, no cloud processing.