How do you merge PDFs on a Mac, and how large is the file afterwards?
With Levati or qpdf, the merged file is as large as the parts combined, at most 0.3% more. With PDFKit, Apple’s PDF framework, the same parts came out 61% to 187% larger.
How large is a merged PDF compared with its parts?
With Levati and qpdf almost exactly as large as the parts together, with PDFKit much larger: three text documents totaling 1.62 MB came to 1.62 MB with Levati and to 4.64 MB with PDFKit.
Levati stays closest to the sum of the parts in every case, and PDFKit is above it in every case.
| Merged | Pages | Sum of parts | Levati 1.0.4 | qpdf | PDFKit |
|---|---|---|---|---|---|
| Terms, Refunds, Privacy | 11 | 1.62 MB | 1.62 MB (+0.12%) | 1.62 MB (+0.22%) | 4.64 MB (+187.0%) |
| Home page and purchase page | 11 | 2.26 MB | 2.27 MB (+0.12%) | 2.27 MB (+0.23%) | 3.65 MB (+61.4%) |
| all six pages | 25 | 4.30 MB | 4.31 MB (+0.18%) | 4.31 MB (+0.28%) | 8.28 MB (+92.4%) |
In brackets, the difference from the sum of the parts.
Why does the file get larger with PDFKit?
Because PDFKit redraws every page and turns text into paths. Merging all six pages, the text operators all but disappeared, the curve operators rose from 24,299 to 247,364, and the page contents grew from 0.72 to 6.96 MB compressed.
PDFKit also rewrites the images, and none stayed byte-identical; it merges duplicates, which saves space but doesn’t make up for the growth of the page contents. qpdf, by contrast, takes the pages over with all their objects as they are (qpdf manual, checked October 29, 2026).
How do you merge PDFs on a Mac?
In the Preview app, View > Thumbnails shows the pages in the sidebar; you drag a whole PDF from the Finder into the sidebar of an open document (Preview User Guide, checked October 28, 2026); Preview was not tested in this measurement. In Terminal, qpdf --empty --pages a.pdf b.pdf -- new.pdf merges whole files.
On the PDF tab, Levati merges two or more dropped PDFs whole and in the order of the list with qpdf, taking over every page, image and link unchanged; the new file sits next to the first one with “zusammengefügt” (merged) added to its name, and the originals stay unchanged.
How a photo gets smaller for an email is covered in How do you make a photo smaller for email on a Mac?.
How was this measured?
Six PDFs were measured on October 29, 2026 on a MacBook Pro with M5 Pro running macOS 27.2.
- Parts: six German pages of levatiapp.com, printed with Chromium 156 through Playwright 1.64.1 as A4 with backgrounds: home page (1.66 MB, 7 pages), purchase page (0.60 MB, 4), privacy (0.82 MB, 6), terms (0.47 MB, 3), refunds (0.33 MB, 2), imprint (0.42 MB, 3).
- Levati 1.0.4: the function
PDFWerk.fuegeZusammenfrom Levati, which runs the bundled qpdf 12.3.2 withqpdf --stream-data=preserve --empty --pages <parts> -- <target>. - qpdf: version 12.4.1 from Homebrew,
qpdf --empty --pages <parts> -- <target>with no further options. - PDFKit: copying each page, inserting it into a new document and writing it with
dataRepresentation(). - Content: page count, text per page and links read with PDFKit, images and page contents compared with
qpdf --json; with Levati, page count, text and links matched the parts, every image was byte-identical, andqpdf --checkfound no error. - Evaluation: file size in bytes; 1 MB is 1,000,000 bytes.
Not measured: scanned PDFs, PDFs from Word, Pages or other apps, and macOS Preview; results may differ there.