Resize PDF

Every PDF page carries its dimensions in points, and that measurement is what a printer obeys. The two dominant standards are close enough to look interchangeable and different enough to cause trouble: A4 is 210 by 297 millimetres, US Letter is 216 by 279. Letter is wider and shorter.

Send an A4 document to a Letter printer and something has to give. Most printers shrink to fit, adding an unequal margin, or print at full size and clip the bottom. Neither is visible until it lands on paper, which is why documents crossing the Atlantic — invoices, contracts, academic submissions — are worth converting deliberately.

The same applies to the less common sizes that specific processes demand: A3 for drawings and posters, A5 for booklets and programmes, Legal for certain US filings, and the fixed photo sizes labs expect.

Once the page size changes, the content has to be placed on it, and the three options behave very differently. Fit scales everything proportionally until it lands entirely inside the new page. Nothing is lost and nothing is distorted; the cost is a band of whitespace on one axis whenever the old and new proportions disagree. This is the right default and the only safe choice for documents where losing an edge would matter.

Stretch fills the new page exactly by scaling width and height independently. There is no whitespace and no lost content, but circles become ovals and text becomes subtly condensed or extended. It is occasionally right for a background or a decorative page and almost never right for anything with words on it.

Centre leaves the content at its original size and places it in the middle of the new page. Moving to a larger page that simply adds margin — useful for adding binding space or a trim allowance. Moving to a smaller page means the content overruns the edges and is clipped, which is the one genuinely destructive combination here.

Text and vector artwork are resolution-independent. They are stored as instructions — draw this glyph at this size, stroke this curve — so a page scaled to any dimension re-renders at full sharpness. Scaling a PDF is not like scaling a photograph, and this is the main reason PDF is used for documents that must print well.

Embedded images are the exception, because they contain a fixed number of pixels. Scaling a page down concentrates them, which usually looks better than the original. Scaling up spreads them, so an image that was exactly sharp enough at A4 will look soft at A3. If a document is destined for a much larger size, the images want to be high-resolution before you start.

File size barely moves in either direction. The same fonts and the same image data are being placed on a differently sized page, so a document resized to half the area is not half the bytes. Compress PDF is the tool for that.

Orientation is chosen alongside size, and the automatic setting is usually the one you want: it keeps each page in the orientation it already had, so landscape charts stay landscape and portrait text stays portrait while both move to the new paper size. Forcing every page to portrait would turn the charts on their side.

Documents legitimately mix orientations, and preserving that is the point. Where a document mixes sizes by accident — pages exported from different systems at different dimensions — resizing everything to one standard is exactly the fix, and is worth doing before printing or binding.

If the aim is fewer sheets of paper rather than a different paper size, N-up PDF places two or four pages on each sheet, which is a different operation and usually the better answer to a long document.