How to Reduce PDF File Size Without Losing Quality: 6 Ways

Why PDFs get so big

Before you compress anything, it helps to know what exactly makes the file heavy. And here's the big secret: nine times out of ten the culprit is the images inside the document, not the text.

That's because text in a PDF takes up laughably little space and, on top of that, is already losslessly compressed. An entire book of plain text fits comfortably in a couple of hundred kilobytes. A single photo from a smartphone, on the other hand, weighs 4–8 MB — drop a dozen of those into a report and the file balloons to tens of megabytes in an instant.

Beyond images, a few other things quietly pile up inside the file:

• Embedded fonts. To make the document look identical on every computer, a PDF carries its fonts with it. Each added font is another 400–600 KB, and a file can hold several.
• Metadata and hidden data. Comments, revision history, thumbnails, invisible layers, form data — all of it is space the reader never needs.
• "Heavy baggage" from editors. When exporting from Photoshop or Illustrator, a PDF sometimes keeps the full editable source of an image "just in case." That doubles the weight for nothing.
• Scans. A scanned page isn't text — it's a high-resolution photograph of a page. The heaviest kind of PDF there is.

Way 1: online compression in a minute

If you need to send the file right now and have no time to fiddle with settings, this is your option. An online PDF compressor does all the dirty work for you: it lowers the resolution of the images, recompresses them and throws out the clutter. All you do is upload the file and download the result.

A document with photos usually slims down 3–10 times. That's almost always enough to fit under the email attachment limit — for most providers that's 20–25 MB.

Way 2: image compression and downsampling

Since images carry the weight, that's where we strike first. Two techniques do the job here, and they work best together.

Downsampling (lowering resolution). Picture this: a photo in the document is stored at 300 ppi — print-shop quality. But an email or a slide deck is read on screen, where even 150 ppi looks perfect. The extra pixels are simply discarded, and the image's weight drops several times over. To the eye, on a monitor, there's barely any difference.

Re-encoding to JPEG. Photos inside a PDF are best stored as JPEG at a reasonable quality. That trims the weight even further while keeping the picture perfectly fine for viewing.

Which resolution should you pick? Base it on how the document will be viewed:

Way 3: strip fonts, metadata and duplicates

Once the images are compressed, you can claw back a bit more by trimming the "ballast." Individually these tricks give less than working on images, but together they can sometimes shave off a meaningful share of the weight.

• Font subsetting. Instead of carrying an entire typeface, the file keeps only the characters actually used. Thousands of unused glyphs go in the bin.
• Cleaning metadata and hidden data. In Acrobat this is "Remove Hidden Information" and "Sanitize Document" — they sweep out comments, history, thumbnails and invisible layers.
• Removing duplicates. If the same logo repeats on every page, an optimizer can store it once and reference it — instead of a hundred copies.
• Skip the "source data." When exporting from graphics editors, uncheck "Preserve Photoshop/Illustrator editing capabilities" — otherwise the PDF drags a full copy of the source inside it.

Way 4: Acrobat and Preview on macOS

If you'd rather stay in a familiar app, the two most popular ones have built-in compression — no extra downloads required.

Adobe Acrobat (Windows and Mac). Open the document and choose File → Save As Other → Reduced Size PDF, or the Optimize PDF tool. The first option compresses in one click; the second gives fine control — you can set a target image resolution, drop fonts and metadata, and see exactly what's taking up space.

Preview on macOS. Free and built into the system. Open the PDF, choose File → Export, and from the Quartz Filter dropdown pick Reduce File Size. The downside: the default filter sometimes compresses too aggressively and softens images, so it's worth eyeballing the result.

Way 5: Ghostscript — one command

For anyone who compresses PDFs regularly or in batches, there's a free tool called Ghostscript. It's a command line, but don't let that scare you: the whole job comes down to a single line, where the key is choosing a quality preset via the -dPDFSETTINGS parameter.

The basic command looks like this (swap in your own file names):

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
   -dPDFSETTINGS=/ebook \
   -dNOPAUSE -dQUIET -dBATCH \
   -sOutputFile=compressed.pdf original.pdf

How much does it actually do? On a real benchmark — a 12-page, image-heavy document with an 8.2 MB original:

Want to push it further? If the document can go black-and-white (a contract with scans, say), converting the images to grayscale buys extra savings: dropping from color to gray cuts the images' own weight by roughly two thirds.

Way 6: the special case of scans and photos

Scanned PDFs are a pain of their own. Every page is stored as a full photograph, so a ten-page scanned document easily weighs tens of megabytes. These call for their own tricks:

• Drop the color. A text document doesn't need color. Converting scans to black-and-white or grayscale slims the file dramatically — it's the biggest single saving for scans.
• Lower the resolution to 150–200 ppi. That's plenty for reading text, and the weight falls several times over.
• Run OCR. Text recognition (OCR) can sometimes shrink the file, but more importantly it makes the text in a scan searchable and copyable — no more retyping by hand.

When to rebuild instead + checklist

Sometimes compression isn't the best path. If the PDF was born from a Word document or a slide deck and you still have the source, it's often simpler to rebuild the file from scratch: place the images at the right (rather than excessive) resolution and export with the correct settings. That way you avoid double compression and get a clean, light result.

A final checklist for shrinking any PDF deliberately:

• ✅ Decide what you're compressing for: screen (150 ppi) or print (300 ppi).
• ✅ Hit the images first — that's 90% of the weight. Downsampling + JPEG.
• ✅ Turn scans to black-and-white and run them through OCR.
• ✅ Trim the rest: font subsetting, metadata cleanup, duplicate removal.
• ✅ Don't recompress the same file several times in a row.
• ✅ Leave text and vectors alone — they're weightless.
• ✅ Open the result, check readability, then send.

And if it turns out the document is easier to edit than to compress, the all formats page has the conversion you need — from PDF to Word to PDF to JPG and back again with JPG to PDF.