Merging copies pages exactly as they are, sizes included, so an A4 report merged with a US Letter invoice and a phone scan gives three page sizes. Resize PDF makes them uniform: choose A4 or Letter and every page’s content is scaled to fit and centred, as vectors, so text stays sharp.
Runs in this tab, on pdf-lib, so your file is read from your own device and never sent anywhere. Check it yourself
How do I fix it?
1Merge as usualCombine the files in Merge PDF. Don’t worry about sizes yet.
2Open the merged file in Resize PDFDrop it on Resize PDF. Mixed sizes are expected.
3Choose one paper sizeUnder New page size pick A4 (210 × 297 mm) or US Letter (8.5 × 11 in). Leave Orientation on Match each page so landscape slides stay landscape.
4ResizePress Resize pages. Each page’s content is scaled to fit the new size and centred, with no stretching.
5Check the white bandsLetter content on A4 paper (or the reverse) leaves thin white bands, because proportions are kept. That is normal and prints correctly.
Why does this happen?
A4 and US Letter in one file. Documents from Europe and most of Asia are A4 (210 × 297 mm); from North America, Letter (8.5 × 11 in). Merged, they differ by about 6 mm in width and 18 mm in height — enough to notice when scrolling.
Scans and photos. A page photographed on a phone or scanned at the scanner’s default size comes out whatever size the image was, often nothing like either paper size.
Slides and spreadsheets. PowerPoint exports are landscape and wide; a spreadsheet saved to PDF may be Legal or Tabloid. Merged with letters, they sit at very different sizes.
Merging is supposed to keep them. A merge that resized pages would scale someone’s contract without asking. Keeping each page exactly is the safe default — and resizing is a separate, deliberate step.
Questions
Why do my PDF pages look different sizes when I scroll?
Because they are: viewers show each page at its real size. A merged file keeps every source page’s dimensions.
Will resizing make the text blurry?
No. Pages are scaled as vectors, so text and lines stay sharp. Scanned pages are pictures and keep their own resolution.
Should I choose A4 or Letter?
The paper the reader will print on: Letter in the US and Canada, A4 almost everywhere else. Courts and some agencies specify one — check their rules.
Can I resize only some pages?
Resize PDF works on the whole file. To resize a few pages, extract them, resize them, and merge them back.