About compress images inside PDF
PDFs can store photographs and scans as image objects with their own encoded streams, dimensions and colour spaces. That allows supported image streams to be replaced without deliberately rewriting the text or vector drawing operators that place content on the page. This tool examines candidate images, asks the browser to decode them and attempts JPEG re-encoding at the selected quality. It does not decode every PDF image format: masked images and unsupported streams can remain unchanged, and each replacement is accepted only if its encoded bytes are smaller. Resolution and quality are different controls. The DPI target can reduce pixel dimensions where placement is recoverable; JPEG quality controls encoding and can affect an image even below that target. A 300 DPI setting is not a pixel-preservation mode, and unknown placement prevents downsampling rather than guaranteeing that no re-encoding occurs. Accepted replacements are declared DeviceRGB, so colour and encoding characteristics can change too. The PDF also undergoes object-stream rewriting and, if enabled, limited cleanup of eight standard Info keys and the catalog XMP reference. That is not secure erasure of all metadata or detached XMP bytes. The complete rewritten candidate is returned only if smaller; otherwise the original bytes, images and metadata remain unchanged. Keep the master and inspect detailed images, searchable text and important document features in the returned file.
How to compress images inside PDF
- 01
Add a PDF containing images
Add one unencrypted PDF, up to 250 MB and 5,000 pages. Presentations, brochures, photo reports and scans may benefit when their image streams can be decoded.
- 02
Choose a resolution target
Choose a target for the intended viewing or print size. Even 300 DPI may remove pixels from larger supported images; no selection disables downsampling for every image.
- 03
Set the quality
Try the initial 65% setting for photographs, or a higher value for diagrams and screenshots. These are starting points, not quality guarantees; inspect fine edges and scanned text.
- 04
Run it and inspect
Check whether the rewrite or original was returned, then inspect the most detailed images. The -compressed.pdf name is used in either case, so it does not prove that any image changed.
What this tool does
- Targets supported image streams without deliberately editing text or vector operators; the PDF is still structurally rewritten
- Separate JPEG quality and DPI targets, without a guaranteed pixel-preservation mode
- Evaluates supported image candidates sequentially; unsupported or masked images may remain unchanged
- Keeps only smaller image replacements, including possible re-encoding of images already below the DPI target
- No upload, so photographs inside confidential documents stay on your device
Limitations worth knowing
Every PDF tool has constraints. Stating them plainly is more useful than discovering them halfway through your work.
- A PDF without supported images may still change size through object-stream rewriting or limited metadata cleanup. No particular saving is guaranteed.
- Accepted JPEG re-encoding is lossy and can compound earlier compression artefacts. Keep the original; repeated runs should start from it rather than a degraded download.
- Screenshots, line art and diagrams suffer more than photographs at the same quality setting, because JPEG handles flat areas and hard edges poorly.
- Accepted replacements use JPEG and DeviceRGB, not the source encoding or a guaranteed preserved colour space. Masked or unsupported images may be skipped. No full rendering or conformance validation is performed.
How your file is handled
This tool runs entirely inside this browser tab. When you choose a file, your browser reads it from your own disk and hands the bytes to JavaScript running on this page — no network request carries your document anywhere. You can confirm that yourself: open your browser’s developer tools, switch to the Network panel, and run the tool. You will see no upload.
Nothing is stored after the fact. Closing or reloading this tab discards the file, the result and everything derived from them, because none of it ever left your machine. Read how local processing works.
Questions about compress images inside PDF
Does this change my text at all?
The engine does not deliberately re-encode text drawing operators or embedded fonts as images. Text that is already inside a scan is part of the image and can soften or acquire JPEG artefacts when a replacement is accepted. The PDF is rewritten, and this tool does not validate every rendering or searchability detail. Check important text and document features in the returned file.
What quality setting should I use?
Use a value as a starting point, then compare the returned file. Photographs may tolerate lower JPEG quality than screenshots, diagrams or small scanned text, whose flat areas and sharp edges can reveal artefacts quickly. Higher settings still use lossy encoding and do not prevent downsampling above the DPI target. Existing compression and the browser codec also affect the result, so no percentage guarantees a particular appearance.
Can I compress the images without losing any pixels?
There is no control here that guarantees that for every image. A 300 DPI target can still downsample larger supported images where placement is measurable. Images below the target, or without recoverable placement, keep their dimensions but may be re-encoded as JPEG; retaining dimensions does not mean retaining all image information. Only smaller replacements are kept, and the original PDF is returned if the whole rewrite is not smaller.
Why did an image look worse than the others?
Possible causes include an image's existing JPEG artefacts, fine edges or small text, a lower effective resolution after downsampling, and changes introduced by the browser's decoder or encoder. Images can start with very different quality, and unsupported ones may not change at all. Compare the original and returned file at the intended size, then try higher settings or keep the original if important detail is lost.
Tools that pair with this one
- Compress PDFMake a PDF smaller by re-encoding its images and cleaning up its internals.
- Extract Images from PDFGet the actual embedded images out of a PDF, at the resolution they were stored at.
- PDF Resolution ReducerAdjust image pixel targets while keeping JPEG quality separate; both steps can lose detail.
- Grayscale Images in PDFApply grayscale to supported image replacements, not every colour in the PDF.
- PDF to JPGRender each page of a PDF as a JPG image, at the resolution you pick.
- PDF Size AnalyzerA byte-level breakdown of where your PDF weight actually is.
Read more about this
- How to compress a PDFCompression is four independent levers, three of them lossy. This guide explains what each one does to your pages so you can choose deliberately rather than guess.6 min guide
- How to reduce PDF file size to meet a limitWritten for the case where a number is imposed on you — an email cap or an upload form. How to converge on a target quickly and what to do when you cannot reach it.6 min guide