How to compress a PDF
- Start with balanced
It is the setting that keeps a scanned page readable while removing most of its weight.
- Run it and read the numbers
The result panel gives the before size, the after size and the percentage saved. Those are measured, not estimated.
- Open the result before you keep it
Check the smallest text on the busiest page. If it has gone mushy, step back a level.
- Stop if the saving is small
A five per cent saving on a text document means there was nothing to compress. That is information, not failure.
Why this matters for exam and study documents
University submission portals commonly cap uploads at 10 or 20 MB, and a phone-scanned handwritten script sails past that easily. Balanced compression usually clears the limit; if it does not, scan again in greyscale rather than compressing twice.
What is kept, what changes, and what this will not do
These are the tools that genuinely alter a document rather than rearranging it, so the trade-offs are real and worth reading before you delete the original.
Kept
- All text, at full sharpness - text is never rasterised here
- Page count, order, size and orientation
- Links, bookmarks and form fields
Changed
- Photographic and scanned images are re-encoded at lower resolution
- Fine detail in diagrams that were supplied as images
- Print quality at strong and extreme settings
Limits
- Text-only and vector documents will barely shrink, because there is nothing image-shaped to remove.
- Compression is not reversible. Keep the original.
Questions and answers
Why did my file barely get smaller?
Because its weight was not images. A text-and-vector PDF is already close to as small as that content can be. Any service that claims a large reduction on such a file is either rasterising your text - which makes it blurry and unsearchable - or measuring something else.
Will compression blur my text?
No. Text is left as text at every level. Only embedded raster images are re-encoded, which is why a scan changes visibly and a typed document does not.
Which level should I use for a scanned exam script?
Balanced. If the portal still rejects it, go to strong and check the handwriting is still legible before submitting. Extreme is for reading on a screen, not for anything that will be marked.
Can I compress the same file twice?
You can, but each pass compounds the quality loss and the second pass saves very little. Go back to the original and use a stronger setting instead.