Reduce PDF file size by fixing the right thing
Most attempts to reduce PDF file size start with a single Compress button and end with a file that is barely smaller. The reason is usually that the button guessed wrong. A scanned contract and a designed annual report can both weigh 40 MB, but the first is almost entirely photographs of paper and the second is mostly fonts, vector artwork and page structure. Squeezing pictures helps the first and does nearly nothing for the second.
PDFSlim measures each document as it is added. The row reads something like "38.2 MB · 91% pictures", and the detail pane draws a bar splitting Pictures from Everything else, with the number of pictures, the space they take and the pixel size of the largest one. You see where the weight is before you decide what to do about it.
Then the settings are the actual operations rather than a preset named Medium, so you can switch off the steps that will not help.
Why is my PDF file so big?
Three things account for nearly every oversized PDF, and the survey separates the first from the rest:
- Pictures stored at camera or scanner resolution. A photo 4000 pixels across placed in a page that will only be read on screen is mostly wasted bytes.
- Page contents a program wrote without compression. Some generators save drawing instructions as plain text, which packs down well with no visible change.
- Hidden data such as the author, the producing software and edit history. Usually small, but worth removing before a file is shared.
Compress a PDF without losing quality
Turn off Re-encode pictures and only the lossless steps run. Repack page contents compresses anything left uncompressed, and Strip hidden data removes the author and editing trail. Every picture stays exactly as it was, and the header changes to Lossless only so there is no doubt.
Text is never converted to an image in any mode, so the slimmed document stays searchable and selectable.
Reduce PDF resolution and picture quality for email or screen
When pictures are the weight, two controls decide the result. Picture quality is a five-step slider from Barely touched through Moderate, where it starts, to Severe. Picture size caps each picture's longest edge at 2400 px for print, 1600 px for screen or 1100 px for email, or leaves pictures at their size.
The size cap is often the bigger lever. Dropping an oversized photo to 1600 pixels removes far more than turning quality down, and nobody reading on a laptop will see the difference. A picture whose new version would come out larger is kept as it was.
