Compress PDF
Reduce PDF size with a lossless structural rewrite: objects are packed into compressed streams and the cross reference tables are rebuilt. Images and text are never re-encoded, and the file stays in your browser the whole time.
Add your PDF
PDF onlyDrop a PDF here or click to browse
Best for files under 50 MB
Result
Add a PDF to startYour optimized PDF will appear here
The original file is untouched. Only the downloaded copy is rewritten.
How to compress a PDF
Add your PDF
Drop in the file you want to make smaller. It is read locally, nothing is uploaded.
Pick an optimization level
Standard keeps the rewrite simple, Maximum adds linearization for a faster first page.
Download the optimized PDF
The file is rewritten in your browser and is ready to download.
Why use Aihangsoft Compress PDF
Lossless, not a re-encode
Only the internal structure is rewritten. No image is recompressed, so page quality stays exactly as it was.
Ready for fast web view
Maximum mode linearizes the file so a browser or reader can show the first page while the rest is still loading.
Stays on your device
The engine is WebAssembly running in the page. Your document is never uploaded, and files up to 50 MB are accepted. Anything larger is refused in the page rather than sent to a server.
What the optimizer actually does
Structural optimization
Objects are collected into compressed object streams, streams that were stored uncompressed are deflated, and the cross reference tables are rebuilt in the compact form the PDF standard allows. Older generators often leave all three of these unoptimized.
Use case: files from older office suites and print pipelinesOptional linearization
Maximum mode rewrites the file so the page tree and the first page data sit at the front. Readers can then draw page one before the full download completes, which matters most on slow connections.
Use case: large reports opened straight from a linkContent carried over as is
Text stays selectable, links stay clickable and bookmarks, form fields and annotations survive the rewrite. The document is never flattened into page images.
Use case: contracts and manuals that must stay searchableHonest about the result
The tool reports the real before and after sizes, and tells you plainly when there was nothing to gain. A PDF that is already packed efficiently can end up slightly larger after the rewrite, and that is reported as a fact, not as a failure.
Use case: deciding whether the new file is worth keepingWhat changes inside the file
Standard or Maximum: which one to pick
- Standard
- Deflates the streams at compression level 6 and packs the objects into object streams. It is the default because it is the fastest option and it does not rearrange the file, so the output is the plainest result a structural rewrite can produce.
- Maximum
- Uses level 9 and adds linearisation, which moves the page tree and the first page to the front of the file so a reader can draw page one before the download finishes. Pick it when the PDF will be opened straight from a link, not when you only care about the byte count.
- Which one is smaller
- Neither, reliably. Level 9 saves a little more than level 6, but linearisation adds a page index and a second copy of some objects, so a linearised file can end up larger than the Standard output of the same document. Both runs are free and unlimited, so if size is the only goal, run the file twice and keep the smaller Change value.
- Which one is faster
- Standard. The engine blocks the tab while it works, and Maximum does more work per file: the stronger deflate pass plus the linearisation pass. On a long document the difference is noticeable, so use Maximum when the reading experience matters and Standard when you are simply trying to get under a size limit.
If the file did not get smaller, work through this list
The Change row already tells you what happened, so read it before trying anything else. A positive number means the document was packed tightly to begin with and another structural rewrite will not help. These are the moves that still can.
Check whether it is a scan
If every page is a photograph of paper, the bulk of the file is already compressed image data, and rebuilding the file structure cannot touch that. Reducing a scan means resampling the page images, which is a different job. Convert the pages to images, lower their resolution, then rebuild the PDF.
Sign: selecting text on a page selects nothingDrop the pages you are not sending
Removing 20 of 60 pages usually beats every compression setting on this page. Split the document first, keep only the range you need, then send the smaller file through the optimizer. Nothing else on this list changes the byte count that much for that little effort.
Sign: the last third of the document is appendicesSplit before you compress a large file
The tool refuses anything over 50 MB inside the page, so a bigger document has to be divided first. Split it into two or three parts, compress each one, and send them as separate attachments or as a folder. Nothing is uploaded while you do this.
Sign: the dropzone reports the 50 MB limitUnlock it first
An encrypted file has to be decrypted before any engine can rewrite it, so this tool stops with a password message. Remove the open password with the unlock tool, compress the unlocked copy, then protect the result again if it still needs to travel encrypted.
Sign: the file prompts for a password in a readerWhat to check before you send the new file
- Text layer
- Open the output and drag across a paragraph. If the text highlights, the layer survived. A structural rewrite never flattens the document, so this should always pass, and it is worth confirming on any file that came from a scanner.
- Links and bookmarks
- Click one internal link and one external one. Both are carried over as ordinary objects, so a broken link means the original was already broken rather than something this tool removed.
- Form fields
- Type into one field and tab to the next. Field values and their appearance streams are kept, but a reader that stores its own copy of a filled form will still show the old values until you reopen the new file.
- Digital signatures
- A signature covers the exact bytes of the original file, so any rewrite invalidates it and this tool is no exception. Keep the signed copy as the record of truth, and have documents signed after they are final rather than before.
Messages you may see, and what they mean
- This PDF is password protected
- The file needs a password before it can be opened. The engine reports this instead of failing silently, so unlock it and run the copy through again.
- This file is larger than 50 MB
- The cap exists because the whole document has to be held in your browser tab memory. Split it into parts, or use a desktop tool if the file must stay in one piece.
- That is not a PDF file
- The extension says PDF but the content is something else, usually a renamed image or an Office file. Convert it to PDF properly first.
- Could not optimize this file
- The document is damaged or uses a structure the engine cannot rewrite. Open it in a reader and export a fresh copy, then try the newly written file instead of the original.
How it works and where your file goes
- Engine
- qpdf 11.7.0 (compiled to WebAssembly) rebuilds the file with object streams, stream recompression and optional linearisation.
- Standard
- Lossless: page content and images are never re-encoded or downsampled.
- Data location
- Everything runs in this browser tab. The file is never uploaded to a server.
- Verify it yourself
- Start a job here and watch the browser network panel: no request carries your file. How to check any online tool.