How to reduce PDF file size without ruining the quality

Your PDF is 38 MB, the email limit is 25 MB, and the upload form on the website you're applying through stops at 10. Shrinking a PDF is easy. Shrinking it without turning every photo into mush takes a little understanding of what makes PDFs big in the first place.

Compress PDF

Reduce a PDF's size with a light, recommended or extreme setting.

What makes a PDF large?

Most of a PDF's weight usually comes from one of three things:

• Images. By far the most common cause. A single photo from a modern phone can be 3–5 MB, and scanners often save pages as huge, high-resolution images. A 40-page scanned document is essentially 40 large photos.
• Embedded fonts. PDFs carry the fonts they use so they look identical everywhere. Usually that's a small part of the file, but documents with many fonts, or fonts embedded in full, can add up.
• Inefficient structure. Files that have been edited and re-saved many times can carry unused objects, duplicated resources and uncompressed data.

That's why a 2-page text document might be 80 KB while a 2-page flyer with photos is 12 MB.

How compression works (and why quality can suffer)

There are two kinds of savings:

1. Lossless clean-up: rewriting the file more efficiently, removing unused resources and compressing the internal data better. Nothing you can see changes.
2. Image downsampling and re-encoding: reducing large pictures to a sensible resolution and saving them as JPEG at a lower quality. This is where the big savings are, and also where quality is lost.

The trick is choosing how far to go for what the document is for.

Which compression level to choose

PDFVelora's Compress PDF offers three levels:

Start with Recommended: it gives a much smaller file that still looks good on screen and when printed at normal sizes. Only drop to Extreme if you still need to get under a limit, and check the result before you send it.

Step by step

1. Open Compress PDF and drop your file on the page.
2. Choose Recommended (or another level as above).
3. Start compressing. When it's done you'll see how much smaller the file got.
4. Download it, open it and zoom into a photo to check it still looks right.

When compressing doesn't make the file much smaller

Sometimes you'll see "This PDF was already well optimized". Common reasons:

• The file is mostly text. Text is already compact. A 300 KB text document can't become 30 KB.
• The images are already compressed or are small.
• Images in special formats (for example some black-and-white scan formats, masks or unusual colour spaces) are left untouched to avoid damaging them.

What else you can do:

• Remove pages you don't need with Delete pages, or send only the relevant ones with Extract pages.
• Split a big document into parts that each fit the limit, using Split PDF.
• Compress the photos before you make the PDF. If you're building a PDF from phone pictures, shrink them first with Compress image, then combine them with Image to PDF.

Avoiding the problem next time

• When scanning text documents, 300 DPI is plenty; higher resolutions mostly add size.
• Scan text pages in grayscale rather than colour when colour doesn't matter.
• In Word or other office apps, when exporting to PDF, choose the "standard" or "minimum size" option for documents meant for screen.

Is it safe to compress a confidential PDF online?

With PDFVelora, files are encrypted in transit and deleted automatically: after 2 hours if you don't have an account, or after 24 hours for account holders unless you choose to save them to My documents. If you'd rather a file never leaves your device, many of the page tools (Merge, Split, Rotate, Delete pages) process smaller files directly in your browser.