How to reduce a PDF's size and what changes when you edit it
A 30 MB PDF that has to go by email or into a form with a 10 MB limit is one of the most common document problems. The fix depends on what takes up space inside the file: almost always images, rarely text. This guide explains how to tell, what QuickToolio's compressor actually does, and what to expect from each everyday PDF operation.
What takes up space inside a PDF
A PDF stores text as text (a few dozen KB per page, even in long documents), vector graphics as drawing instructions and photos as embedded images. Those images are what drive the size: a scanned contract or a catalogue with camera-resolution photos can take several MB per page, whereas a 100-page report exported from Word without photos usually stays at one or two MB.
- Scans: each page is a full photo of the sheet; this is the case that shrinks most when compressed.
- PDFs exported with unresized phone photos: images of 4000 px or more inside an A4 page.
- Fully embedded fonts: they add from tens of KB to a few MB, but they're rarely the main problem.
- Accumulated revisions: some programs save each edit by appending data to the end of the file instead of rewriting it.
What QuickToolio's PDF compressor does
It doesn't turn pages into images: it walks the PDF's internal objects, finds JPEG images in RGB colour and re-encodes them at lower quality, leaving text, vectors and document structure untouched. Text stays selectable and searchable.
- High quality: JPEG at 82% without changing image resolution.
- Balanced: JPEG at 60% and, if an image is larger than 2000 pixels on its longest side, it's scaled down to that.
- Small file: JPEG at 42% and at most 1400 pixels on the longest side.
- If a recompressed image isn't smaller than the original, the original is kept.
Greyscale, CMYK, indexed-palette and ICC-profiled images are left alone so their colour isn't altered; that's why a print-ready (CMYK) PDF may shrink only a little.
Why a PDF sometimes barely gets smaller
- It's a text PDF with no photos: there's nothing heavy to recompress.
- It was already optimised: another tool reduced its images before.
- Its images aren't RGB JPEGs: black-and-white scans (CCITT or JBIG2), CMYK or greyscale images.
- The weight is in embedded fonts or file attachments inside the PDF, which the compressor doesn't modify.
In those cases, converting the pages to images and rebuilding a PDF can weigh even more, and it loses selectable text. If the size limit is strict and the PDF has few pages, splitting it and sending several parts is sometimes the better option.
Merging, splitting and extracting pages don't change the weight per page
Merging several PDFs copies the pages as they are: the result weighs roughly the sum of the originals. Splitting or extracting pages doesn't recompress anything either; each part weighs what its pages weigh, though shared resources (a font, for instance) may be repeated in each file. In both cases a new document is created, so the original's side-outline bookmarks and metadata don't carry over.
Converting to images or text: what you lose
Turning a PDF into JPG renders each page at roughly twice its nominal resolution: handy for sharing as an image, but the text can no longer be selected. The other way round, extracting text only works if the PDF has a text layer; a scan needs optical character recognition (OCR).
Passwords, metadata and damaged files
Protecting a PDF with a password encrypts it with AES-256: without the password it can't be opened or recovered, so keep it in a password manager. Removing a password requires knowing it. Before sharing a document, it's worth checking its metadata (author, originating program, dates) and removing it if it shouldn't be visible; note that embedded photos keep their own EXIF data. If a downloaded PDF won't open, it's often an incomplete download or a shifted internal table that can be rebuilt.
Which profile to choose for each destination
- For printing or archiving: high quality, or don't compress.
- For email or a web form: balanced; 2000 pixels still read well on screen.
- For a very strict limit or phone-only viewing: small file, checking that scanned text is still legible.
- If the heavy part is a single photo you're about to put in the PDF, it's more effective to shrink it first with the image-to-target-size tool.
Frequently asked questions
Does compressing a PDF make the text blurry?
Not with this method: only JPEG images are recompressed. Text and vectors are untouched, so they stay sharp at any zoom.
How much does a scanned PDF shrink?
It depends on how it was scanned. A colour scan saved as high-quality JPEG usually shrinks a lot with the balanced profile; a black-and-white one compressed with CCITT or JBIG2 barely changes, because those images aren't recompressed.
Why won't my PDF from Word get smaller?
Because it's probably almost all text and fonts: it's already small for its content and has no JPEG images to recompress.
Are links or bookmarks lost when compressing?
No: the compressor modifies the original PDF and only replaces image data. Merging, splitting or removing metadata do create a new document without bookmarks.
Are my PDFs uploaded to a server?
No. All these tools read and write the PDF in your browser; the file never leaves your device.