Why is my PDF so big, and how do I make it smaller?

Start by finding out what is heavy

Shrinking a file blindly wastes time, because the right fix depends on the cause. PDF Information shows the page count, file size, PDF version, page sizes, fonts used, the number of embedded images and the number of attachments. Nothing is uploaded, so you can inspect confidential files safely.

Divide the file size by the page count. A few hundred kilobytes per page is normal for a text document. Several megabytes per page almost always means full-page images, which is what scanned or photographed pages are.

The usual suspects

Nearly every oversized PDF falls into one of these categories.

• Scanned pages saved as high-resolution images, often 300 DPI or more in colour, even when the page is only black text on white.
• Photographs inserted at their full camera resolution and then displayed small on the page, so most of the pixels are never seen.
• Screenshots or exports with unnecessary transparency or very large dimensions.
• Many fonts embedded in full, typically in files assembled from several sources.
• Attachments or embedded files carried inside the PDF, which the information view counts separately.
• A very high page count, which is simply a lot of content rather than a fault.

Size limits you are likely to hit

Limits vary and change, so read the wording of the service you are sending to. As a rough guide, many email providers cap attachments at around 20 to 25 MB in total, including encoding overhead, so a file of 18 MB may already be too much once other attachments are counted.

Application portals, government forms and learning platforms often set their own ceilings, commonly somewhere between 1 and 10 MB per file, and some restrict the number of pages as well. If a portal states a limit, aim comfortably below it rather than at it.

Fix 1: compress the images

When the cause is images, Compress PDF is the direct answer. It re-encodes embedded JPEG images at a lower resolution and quality and rewrites the file structure efficiently, while text and vector graphics stay sharp and selectable. It shows original size, new size and percentage saved.

Try Recommended first. Move to Maximum compression only if you still miss the limit, and keep the original so you can go back. If the tool reports that the file was already well optimized, compression has nothing left to give and you need one of the other options below.

Fix 2: reduce colour or content

For a colour scan that will be read or printed in black and white, PDF to Grayscale can help. It renders each page to an image at 150 or 200 DPI and rebuilds the PDF, so the text becomes non-selectable image content; run OCR PDF afterwards if you need to search it.

If only part of the document is required, remove the rest. Extracting or deleting pages is often the biggest saving of all, because pages you do not send weigh nothing.

Fix 3: rebuild from the source

If you still have the original Word, presentation or design file, exporting again with a lower image quality setting is usually cleaner than post-processing. Replacing an oversized photo before export gives a better result than compressing it inside the PDF afterwards.

As a last resort for image-based documents, PDF to JPG can render pages at 72 or 150 DPI, and the images can be rebuilt into a PDF. This is coarse, it makes text non-selectable and it cannot be undone, so use it only when nothing else brings the file under the limit.

When you cannot get under the limit: split

Sometimes the content simply is that large. Split PDF has a mode that splits by maximum file size: you enter a target in MB and it divides the document at page boundaries. The target is approximate, and a single page larger than the target stays whole. Several outputs arrive as one ZIP, so you can send the parts separately.

After any of these fixes, open the result and check that pages, images and small print are still acceptable before you send it.