How to reduce a PDF's file size
By Dexaloop · Updated 27 October 2026 · Checked against the sources listed below
To reduce a PDF's file size, shrink the images inside it. In most large PDFs, photos and scanned pages take up nearly all the space, and they are often stored at a far higher resolution than anyone will see on screen. Lowering their pixel size and saving them with stronger JPEG compression usually cuts the file by a large share, while the text stays sharp. If that is not enough, remove pages you do not need or split the file into parts.
Why PDFs get big
Adobe, which created the PDF format, names two main causes. The first is fonts: "PDFs can be oversized because one or more fonts have been embedded and subset inside that specific PDF file," and "adding a single font to a PDF document can sometimes increase the file size substantially." The second is images: "The overall resolution and bit-depth of an image can directly impact the overall file size."
Fonts are embedded so the document looks the same on every device, which is why you usually want to keep them. Images are where the waste tends to be. A phone photo dropped into a report, or a page scanned at high resolution in full color, carries far more pixels than the page needs.
Adobe also points to a third, quieter cause: how the file was saved. Repeated edits can be appended to the file rather than rewritten, and Adobe recommends a save that "writes an entirely new file as opposed to adding changes to an already existing file."
The arithmetic of a scanned page
An A4 page is 8.27 by 11.69 inches. Scanned at 300 dots per inch, it becomes an image of about 2,480 by 3,508 pixels, which is roughly 8.7 million pixels. In full color each pixel needs 3 bytes before compression, so the raw picture is about 26 MB for a single page. JPEG compression brings that down a lot, but a 20-page color scan can still run to many megabytes.
Now shrink the picture. If the longest side is reduced from 3,508 pixels to 1,800, each side is about 51% of the original, and the pixel count falls to about 26% (0.51 times 0.51). That is roughly a quarter of the data before JPEG compression even starts, and 1,800 pixels tall is still sharp on a laptop screen. That is the core of what PDF compression tools do.
What you are usually trying to get under
| Where it is going | Limit | Source |
|---|---|---|
| Gmail attachment (personal account) | 25 MB | Google Gmail Help |
| Outlook, internet email account (POP3, IMAP) | 20 MB default (20,480 KB) | Microsoft Learn |
| Outlook with an Exchange mailbox | 10 MB by default, set by the administrator | Microsoft Learn |
| Greenhouse resume parsing | 2.5 MB | Greenhouse Support |
| Government and job portals | Varies; often stated in KB next to the upload button | Check the form |
Two details matter. Gmail says that when attachments exceed its limit, it "automatically removes the attachment and adds it as a Google Drive link in the email," so your recipient gets a link instead of a file. And Microsoft states the Exchange limit as "10 MB (10240 KB)", which shows the 1,024-byte kilobyte; some upload forms use 1,000 bytes instead. If a form says 200 KB, aim for 190 so you are safe either way.
Ways to shrink a PDF, from safest to most drastic
- Compress the images. Reduce their pixel size and JPEG quality. Text, fonts and line drawings are left alone. This gives the biggest drop for scans and photo-heavy files.
- Save a fresh copy. Use "Save As" or export again rather than saving over a heavily edited file, so old revisions are not carried along.
- Remove what nobody needs. Blank pages, duplicate scans and large attachments can go. Use a split tool to keep only the pages you need.
- Re-create from the source. If you have the original Word or Google Docs file, export the PDF again with a "smaller file" or "minimum size" option. A PDF made from the source is far lighter than a scan of a printout.
- Rescan at a sensible setting. Scanning at 150 dpi instead of 300 cuts the pixel count to a quarter, and a grayscale setting needs one byte per pixel instead of three. Check that the smallest print is still readable.
- Split the file. If a portal allows several uploads, send two smaller parts rather than over-compressing one.
Common mistakes
- Compressing a signed document. Any change breaks a digital signature. Compress first, sign after.
- Over-compressing scans of small print. Bank statements and ID documents need to stay legible. Zoom to 100% and read the smallest line before you send.
- Compressing the same file again and again. Each JPEG pass loses a little more detail. Always start from the original.
- Trusting a tool that uploads private files. ID cards, payslips and medical letters are better handled by a tool that works on your own device.
- Expecting text-only PDFs to shrink much. If the file is mostly text and fonts, there are no images to reduce, and the savings will be small.
Doing it in your browser
Our Compress PDF tool runs in your browser, so the file is not uploaded to a server. It lowers the pixel size and JPEG quality of the pictures inside the PDF and leaves text, fonts and drawings untouched. You can choose a level or type a size limit in KB, and it will try each level until the file fits, or tell you the smallest size it could reach. It never hands back a bigger file than you gave it. Password-protected files need to be unlocked first.
Compress a PDF in your browser: pdf.dexaloop.com/compress-pdf/. Free, no sign-up, and it runs on your device.
Questions
Why is my scanned PDF so much bigger than a typed one?
A scan stores every page as a picture, so even a page of plain text carries millions of pixels. A PDF made from a word processor stores the words as text, which takes very little space.
Will compressing a PDF make the text blurry?
Real text and vector drawings are not affected by image compression, because they are not images. Scanned pages are images, so heavy compression can soften them. Check a page at 100% zoom before sending.
How do I get a PDF under exactly 100 KB or 2 MB?
Compress the images first, then check the size. If it is still too large, compress more strongly, remove pages that are not needed, or split the file. Aim slightly below the limit, because some sites count 1 KB as 1,000 bytes and others as 1,024.
Is it safe to compress a signed PDF?
Any change to a digitally signed PDF makes the signature show as invalid. Compress before signing, or ask for a new signed copy.
Can a PDF be made smaller without losing any quality?
Sometimes, by removing unused items or saving a fresh copy rather than appending changes. Adobe notes that saving can write an entirely new file instead of adding changes to the existing one. Large savings almost always come from images, which means some loss.
Sources
- Adobe Acrobat: Why is my PDF so big?
- Google Gmail Help: Attachment size limits
- Microsoft Learn: Attachment size exceeds the allowable limit error (Outlook)
- Greenhouse Support: Unsuccessful resume parse
- Dexaloop Compress PDF tool page
This guide is general information, not legal, tax or financial advice. Rules change; check the official source for your own case. Found a mistake? Email support@dexaloop.com.