Why page size matters
A document made for US Letter prints with odd margins on A4 paper, a poster-size PDF will not fit a standard printer, and a form that must be submitted on a specific paper size will be rejected if it is not exactly that size. Resizing changes the paper size of every page so it matches what you need.
Choosing a size
Resize PDF offers a searchable list of more than 60 standard sizes in groups: ISO A series (A0–A10), ISO B and C series, JIS B series, US sizes such as Letter, Legal, Tabloid, and the ANSI C, D, and E sheets, architectural sizes, and photo and other formats. Pick one and every page is resized to it. There is no custom-size option.
How the pages are resized
Each page is scaled to fit inside the new paper size without being stretched, centered, and placed on a white page. If the new size has a different shape from the original, you get white space on two sides rather than distortion. Pages are not cropped, so nothing is lost.
To do this, PDF Studio redraws every page as an image at a high resolution. The result looks like the original, but because the pages are now pictures, the text is no longer selectable or searchable and the file can be larger than the original. If you need searchable text again, run OCR PDF on the resized document.
Alternatives for specific cases
When you just want to print on a different paper size, the “fit to page” or “scale to paper” setting in your print dialog changes the size at print time with no loss. Use Resize PDF when you need a new PDF file of the right size. To trim borders without changing the page size, use Crop PDF. The conversion runs in your browser, so your file is not uploaded.