How to compress PDFs and images

Before you start

Keep an untouched original. For images, decide whether the destination needs print detail or only a screen preview.

How to do it, step by step

1. Add the PDF or image you want to make smaller. Keep the original so you can compare the two versions.
2. Choose a compression strength and process the file. Start with a moderate setting if small text or image detail matters.
3. Compare the new file size and appearance. Download the result only if the trade-off is useful.

Check the saved file

Compare readable text, fine lines and faces at full size, not just the download size.

Why a compressed file can be bigger

JPEGs and already-optimized PDFs may contain very little redundant data. Re-encoding can add overhead instead of saving space. Try a stronger setting on a copy. If quality suffers or the result grows, keep the original; compression is not a guarantee of a smaller file.

Work backward from the upload limit

Suppose an application form accepts a file smaller than 5 MB and your document is 8 MB. Make one compressed copy, inspect it, and compare its actual size with the limit. If it is still too large, try a stronger setting. Do not keep recompressing a low-quality output: start each attempt from the original so you can compare trade-offs fairly. Exact output size is not guaranteed.

Scanned pages and text-only PDFs behave differently

A scan may be large because each page is a photograph. Reducing image detail can save space, but it can also make small writing harder to read. A PDF made mostly of text may already be compact. If compression produces little saving, removing unnecessary pages can help—but only remove content that the recipient does not need.

A practical quality check

1. Read the smallest text at normal viewing size, especially dates, account numbers and footnotes.
2. Zoom in on signatures, stamps and thin table lines. Check any page whose image quality was already poor.
3. Keep the original until the recipient has accepted the compressed version. If the new file is larger or less useful, send the original another way instead.