A PDF built for A4 paper doesn't line up right when it's printed on US Letter, and plenty of forms, portals, and print shops will reject a file outright if it isn't the size they expect. LockerPDF's Resize PDF tool converts every page of a PDF to A4, US Letter, or US Legal size entirely in your browser. The file is read, resized, and rebuilt on your device -- nothing is uploaded to a server.
A4, Letter, and Legal aren't interchangeable
A4 is 595.28 x 841.89 points, or about 8.27 x 11.69 inches -- the standard paper size across most of the world outside North America. US Letter is 612 x 792 points, 8.5 x 11 inches, the default in the United States and Canada. US Legal is 612 x 1008 points, 8.5 x 14 inches, used mainly for contracts and legal filings in the US. A point is 1/72 of an inch, the standard unit PDF page dimensions are measured in.
The practical problem is that A4 and Letter are close in size but not the same shape. A4 is narrower and taller relative to its own width than Letter is. A document formatted to fill an A4 page will have its content run slightly wide or fall slightly short when the page itself is swapped for Letter dimensions without also rescaling what's on it -- which is exactly what a plain "change the page size" operation, done wrong, would produce.
How to resize a PDF
- Go to the Resize PDF tool and upload the PDF you want to convert.
- Choose a target size: A4, US Letter, or US Legal.
- Click "Resize PDF."
- Download the result.
The target size applies to every page in the document in one pass. There's no per-page selection -- if you only need to resize a subset of pages, split the file first or extract the pages you need.
Content is scaled to fit, not stretched
This is the part worth understanding before you rely on the tool: resizing a PDF's page dimensions and resizing what's drawn on that page are two different operations, and doing only the first one badly distorts everything on the page or clips it off entirely. LockerPDF's Resize PDF tool does both together. For each page, it works out a single scale factor that fits the page's existing content within the new target dimensions while keeping its original width-to-height ratio exactly intact -- so nothing gets squashed narrower or stretched taller just because the target page shape doesn't match the source.
If the source page's proportions don't line up exactly with the target size -- which, given A4 and Letter aren't quite the same shape, is normal -- the scaled content is centered on the new page with even margins on the sides that have extra room, rather than distorted to fill the page edge to edge. This is the same letterboxing approach LockerPDF's Multiple Pages per Sheet tool uses when fitting pages into a grid cell of a different shape.
This is also a vector operation, not a rasterization. The tool uses pdf-lib to scale and reposition each page's actual content -- text-drawing operators, vector graphics, embedded images -- as a unit, then sets the page's new dimensions. At no point is the page rendered to a pixel grid and pasted back in. Text stays selectable and searchable after resizing, and any images on the page keep their original resolution; scaling a page down or up doesn't blur or degrade what's on it the way flattening it to an image would.
Why margins show up after converting between A4 and Letter
Because A4 and Letter have different proportions, converting between them will usually add a thin margin on one pair of edges even though the whole page fills most of the target size. Going from A4 to Letter, for example, content that filled A4's taller, narrower shape leaves a small margin at top and bottom once it's fit into Letter's slightly wider, shorter shape. This isn't a bug or a cropping side effect -- it's the unavoidable result of two paper sizes not sharing the same aspect ratio, and it's the same thing that happens if you print an A4 document on a Letter printer using "fit to page" instead of "stretch to fill."
Common reasons to resize a PDF
- Submitting to a US institution: many US universities, government forms, and print services require Letter, and will bounce an A4 submission or print it with an offset margin.
- Submitting internationally: the reverse is just as common -- forms and publishers outside North America often expect A4 and won't accept Letter as-is.
- Legal filings: contracts, court documents, and similar paperwork in the US are frequently required to be Legal size rather than Letter.
- Matching a printer or print shop's stock: if the only paper on hand or on offer is a different size than the document was built for, resizing ahead of time avoids a printer defaulting to an awkward auto-scale.
Resizing vs. cropping vs. combining pages
Resizing is not the same operation as cropping. Crop PDF trims away part of a page -- it adjusts the visible boundary and discards whatever falls outside it, without touching the scale of what remains. Resize PDF does the opposite: it keeps all of the existing content and scales it as a whole to fit a new page size, adding margins rather than cutting anything off. Use Crop when you want to remove excess white space or an unwanted strip along one edge; use Resize when the page itself needs to be a different standard size.
It's also worth sequencing correctly if you're combining pages. Multiple Pages per Sheet arranges several original pages onto each output sheet, but its output sheet size always matches whatever size your source PDF already is -- it doesn't have its own size picker. If you need a combined, multi-page-per-sheet document in a specific paper size, resize the source file first, then run the resized file through Pages per Sheet.
FAQ
Are my files uploaded anywhere when I resize a PDF?
No. Resizing runs entirely in your browser using JavaScript and pdf-lib. Your PDF is read from your device, scaled and rebuilt in memory, and handed back to you as a new file. It's never sent to a server.
Will my content get stretched or cropped to fit the new page size?
No. Each page's content is scaled up or down as a whole, keeping its original proportions intact, then centered on the new page with even margins if the shapes don't match exactly. Nothing is squashed, stretched, or cut off.
Does resizing affect text or image quality?
No. Pages are resized as vector content -- the same text-drawing instructions and image objects, just scaled and repositioned -- rather than rendered to a pixel grid. Text stays selectable and searchable, and images keep their original resolution.
What's the actual difference between A4, US Letter, and US Legal?
A4 (8.27 x 11.69 in) is the standard size across most of the world outside North America. US Letter (8.5 x 11 in) is standard in the US and Canada. US Legal (8.5 x 14 in) is longer than Letter and used mainly for contracts and legal filings in the US.
Can I resize a PDF where the pages aren't all the same size already?
Yes. Each page is scaled independently based on its own original dimensions, so a document with mixed page sizes -- a scanned insert next to a normal page, for example -- still ends up with every page converted to the same target size.