Compress vs resize: two ways to make a PDF smaller

Two tools are commonly confused when the goal is to make a PDF smaller: compression and resizing. They are complementary, not the same operation, and understanding which one fits your situation saves time and avoids quality trade-offs you did not intend to make.

What compression does

Compression restructures the PDF's internal data. It rewrites how objects — text, images, fonts, cross-reference tables — are stored inside the file, and removes redundant or duplicated data that accumulated through editing, merging, or repeated saving. Crucially, it does not change the visual content of the document: the pages look identical after compression. Text remains fully selectable. The file simply becomes a leaner, more efficient version of the same document.

What resizing does

Resizing changes the physical page dimensions of the document — from A3 to A4, from US Letter to custom, or from a non-standard size to a print-standard one. It does not directly target file size; it targets page dimensions. Content is scaled proportionally to fit the new dimensions, so nothing is cropped. Resizing is primarily a layout operation: you use it when you need every page to be a consistent, standard size for printing, binding, or submission to a print shop or document portal that requires a specific format.

When to compress

• The file is the right page size but too large for email or an upload portal.
• The document has been merged or edited several times and may have accumulated redundant internal data.
• You are distributing the final version and want to optimise file size before sending.
• Text quality must be preserved — compression keeps text crisp.

When to resize

• The document has mixed page sizes that need to be standardised before printing.
• The source file was designed at a non-standard size and the recipient or print shop needs A4 or US Letter.
• You need to scale content up or down to a specific page dimension.
• File size is not the goal — resizing is not a reliable file-size reduction technique.

Using them together

Resize first to get the page dimensions correct, then compress the resized document to optimise the file. Running them in this order means you are compressing the final, correctly sized version rather than an intermediate file. Between the two operations, you will usually arrive at a document that is both the right dimensions and the right file size for its intended destination.

A note on image-heavy documents

Neither compression nor resizing will significantly shrink a PDF whose bulk comes almost entirely from high-resolution embedded images, such as a multi-page photo book or a batch of scans saved at 600 DPI. In those cases, the only reliable way to substantially reduce file size is to re-export the source at a lower image resolution — 96–150 DPI is adequate for on-screen use, while 300 DPI covers most print requirements. If you do not have access to the original source files, our Compress PDF tool applies the best optimisation possible to the images that are already embedded.