How to Reduce PDF File Size: Make a PDF Smaller on Any Device

Text costs very little in a PDF. A hundred pages of plain text can be a few hundred kilobytes. What makes PDFs big is almost always images, and a scanned document is nothing but images, one full-page picture per page.

Fonts and leftover data add the rest. Most PDFs embed their fonts so the text looks the same everywhere. Usually only the characters used are embedded, but a full font, especially one for Asian scripts, can add megabytes. Files edited many times can also carry old versions of pages, because each save may append changes instead of rewriting the file.

PDFToolz Compress PDF runs in your browser on any computer or phone. The PDF is processed on your device and never uploaded, and there is no account, watermark or usage limit. If the result isn't smaller than your original, the tool gives you the original back instead of a bigger file.

Job portals, visa applications and university forms often cap uploads at 100 KB, 200 KB or 1 MB. Guessing a compression level until one fits is slow. PDFToolz Compress PDF to Size takes the target and searches for the best quality that fits under it.

It tries settings that keep the text selectable first. Only if none of those fit does it save the pages as images, at the highest quality that still fits. If no setting reaches the target, it tells you and gives you the smallest file it could make. At that point, remove or split off pages and try again.

Preview, the PDF viewer built into macOS, has a Reduce File Size Quartz filter. It compresses the images in the file and needs no extra software.

The filter is a one-click preset with no quality setting. Apple notes that the compressed PDF may be of lower quality than the original. Zoom in on photos and small print before you send the file, and keep the original. If the quality drops too far, use Compress PDF with the Recommended level instead.

On Windows, the simplest route is a browser tool. PDFToolz Compress PDF works in Edge, Chrome or Firefox with nothing to install, and the file stays on your PC.

If the PDF came from Word, you can often get a smaller file by exporting it again. In Word for Windows, choose File > Save As or Save a Copy, pick PDF as the file type and set Optimize for to Minimum size (publishing online). Microsoft suggests that option when file size matters more than print quality.

If you pay for Adobe Acrobat, its Compress a PDF tool and Reduced size PDF command also work. Our guide to compressing a PDF in Adobe covers those steps and why the free Adobe Reader can't do it.

On a phone, the fastest way is to open PDFToolz Compress PDF in Safari or Chrome, pick the PDF from Files or your downloads and compress it there. The work happens on the phone itself, so nothing is uploaded.

The Compress command in the iPhone Files app makes a ZIP archive, which saves little on a PDF and has to be unzipped by the recipient. For real PDF compression, the Shortcuts app has an Optimize File Size of PDF action, added in iOS and iPadOS 16. Apple describes it as compressing the images inside a PDF. Build a shortcut that takes a PDF, runs that action and saves the result, then run it from the Share sheet. Like Preview's filter, it doesn't let you set the quality.

On Android, use a browser tool the same way, or an app you already trust. Check whether an app uploads your file before using it on private documents.

When compression alone isn't enough, reduce what's in the file. Color takes more space than gray, and every page you drop removes its images and text.

PDFToolz Grayscale PDF renders each page as a grayscale image and rebuilds the PDF from those images. Color scans and photo-heavy files usually shrink. A text-only PDF can get bigger, because its text becomes images. Either way, text is no longer selectable afterwards. The result screen shows both sizes, so you can see which you got.

Savings depend on what's inside the PDF. Image-heavy files and scans shrink a lot. Files that are mostly text are often close to their minimum size already. Lossy methods can't be undone, so always keep the original.

If a compressor barely changes the size, the file usually has little left to remove. A text-only PDF exported from Word or Google Docs is already compact, and compressing it again saves only a few percent. Only turning pages into images, or removing pages, will shrink it further, and the first makes it worse to read and search.

Some images are left alone. PDFToolz Recommended skips small images, CMYK images, black-and-white scans and some images with masks, so a file full of those may not shrink much. A PDF that needs a password to open has to be unlocked first with Unlock PDF. For files you create yourself, the best fix is at the source. Scan text documents in grayscale or black and white at about 300 DPI instead of full color, and resize photos before you put them in a document.