Merging PDFs sounds trivial until you actually need it done right: the wrong page order, a dropped bookmark, or a "quality loss" you can't quite explain. Here's exactly what happens to your files during a merge, so there are no surprises.
What "Merge" Actually Does
A real PDF merge doesn't touch the content of your pages at all — it copies each page object wholesale from the source files into a new document container and repackages them in order. Nothing gets re-rendered, re-compressed, or re-encoded. That's why merged output is byte-for-byte identical in quality to the originals: there's no operation happening that could degrade anything, unlike, say, image conversion where a genuine transformation occurs.
How to Merge PDFs on ILoveConvert
- Go to ILoveConvert Merge PDF
- Click to upload your PDF files, or drag multiple files at once. You can upload up to 20 PDFs in one merge job.
- Drag the files in the upload list to arrange them in the order you want in the final document
- Click Merge PDFs
- Download the single combined PDF
Controlling Page Order
The order of files in the upload list determines the page order in the merged PDF. File 1's pages come first, followed by File 2's pages, and so on. If you need a specific page order:
- Name your files numerically before uploading:
01_intro.pdf,02_chapter1.pdf,03_appendix.pdf - Use the drag-and-drop reorder handles in the upload panel to rearrange after uploading
- If you need to rearrange individual pages across files, use our Split PDF tool first to extract pages, then merge them in your desired order
Merging PDFs With Different Page Sizes
ILoveConvert handles mixed page sizes — you can merge an A4 document with a Letter-size document without any issues. The resulting PDF will contain both page sizes as they are. If you need all pages to be the same size for printing or presentation, you can print the merged PDF to a new PDF and specify a single page size.
What Gets Preserved During Merge
- All text content, fonts, and formatting
- Images at their original quality
- Page dimensions and orientation (portrait/landscape per page)
- Hyperlinks and internal document links
One thing that doesn't carry over: bookmarks/outline entries. Copying page objects between documents doesn't bring the source file's navigation tree with it — if you need a bookmarked table of contents in the final file, add it afterward in a PDF editor.
Merging Secured or Password-Protected PDFs
PDFs with a user password (required to open the file) cannot be merged until free. Remove the password first by opening the PDF and re-saving without security, or using a PDF free tool. PDFs with only an owner password (restricts editing but not opening) can usually be merged without issues.
Best Practices for Large Merge Jobs
- Compress each PDF before merging if the combined file size is a concern — our Compress PDF tool can reduce individual files by 30–60% before you merge them
- For more than 20 files, merge in batches of 20, then merge the resulting combined files together
- After merging, add bookmarks in a PDF editor (Adobe Acrobat, PDF-XChange) so readers can navigate to each section
- Test the merged PDF by scrolling through it and confirming page order before sharing
One limit worth planning around: each individual file caps at 50 MB, and a single job handles up to 20 files. Neither limit is arbitrary — beyond that, browser upload reliability starts to suffer more than the merge logic itself. If you're combining more than 20 documents, merge in two batches and then merge the two results together; the output quality is identical either way, since it's the same page-copy operation regardless of how many rounds it takes.