How to fix a merged PDF with pages of different sizes

Merging PDFs: pages at half size and the trick that fixes it

Why does merging several PDFs produce a document where some pages are normal size and others are shrunk to half? It's the problem that shows up when files scanned by different people are combined. The specific case: a final document of 45 pages assembled with the free version of PDFSAM, part of which arrived by email —each sender with their own scanner and settings— and part of which the person concerned had digitized themselves with their phone, at different times and distances. On their own, each file looked fine. Together, the result was hard to present anywhere.

Why merged PDFs end up with pages of different sizes

According to the person's own explanation, the problem wasn't the software but the different sizes and formats of the originals. Each file keeps the page size it was created with: a different setting on each sender's scanner, a different framing when digitizing with a phone. When you merge them, those jumps are visible at a glance.

That's why the second attempt, with a different program, repeated the same disaster. The problem, according to their theory, traveled inside the PDFs, not in the application gluing them together.

Which tools merge PDFs without ruining the formatting

The list of options is long and nothing out of the ordinary. On Linux, the pdfunite utility from the poppler package does the job with a single console line, and some warn that recent versions of ImageMagick restrict PDF processing for security reasons, forcing you to tweak its permission policy. On Windows, a PowerShell module solves the same thing from the terminal. On Mac, just select the files and use the quick action for creating PDFs.

For those who prefer windows and buttons, the list includes LibreOffice, PDFGear, PDFTK Builder Enhanced and a couple of desktop suites aimed at office environments. Most handle the merging fine; the size problem still depends on the originals.

Is it safe to upload a PDF to a website to merge it?

Here the consensus breaks less than it seems. Online platforms are the most cited for convenience, and also the ones that raise suspicion: we don't know who's behind them or where those files end up, one participant warns. For documents with personal data —a bank statement, for example— the repeated recommendation is to use installed software and work offline.

The debate isn't technical, it's about trust. A local utility does the same thing and doesn't require handing the document over to a third party.

How do you fix an already-merged PDF with uneven pages?

Here comes the interesting part. With the file already assembled and open, the solution that worked was a virtual printer: Microsoft Print to PDF. The document came out flat, with all pages evened out and a presentable look. The operation converts the file into a uniform image and, along the way, removes the size differences carried over from the originals.

It's not magic, it's rasterizing and recomposing.

The uncomfortable conclusion for the software crowd: the tool matters less than knowing what you're feeding into it. With mismatched source sizes, any merge comes out crooked. With a flattening step beforehand, even a disaster can pass for a magazine.