Merge PDFs

Merging PDFs without breaking the document

Combining PDFs sounds like stapling, and most of the time it behaves that way. The complications show up in the parts of a PDF that are not page content: the outline tree, form field definitions, and the page boxes that a printer reads. Knowing which of those survive saves you a reprint or a rejected filing.

Order is decided before you merge, not after

The tool writes files in the sequence shown in the list. Every page of the first file lands before the first page of the second. There is no page level shuffling inside the merge step, so build the order in the list first. If a document needs to be broken up before it joins the rest, run it through Split PDF and merge the part you kept.

A habit worth adopting for filings and tender packs: name your source files with a numeric prefix such as 01-cover, 02-statement, 03-appendix. Your file picker then hands them over already ordered, and the merged result matches the index you wrote.

What carries over and what does not

• Carries over. All page content: text and its selectable layer, vector graphics, embedded images, and per page size and rotation.
• Does not carry over. The outline bookmark tree. A merged file opens without the chapter list the originals may have had, so long documents benefit from a printed table of contents page.
• Carries over unreliably. Interactive form fields and some annotation types. Two documents that both define a field called signature cannot both keep it in one file. Check any form after merging.
• Rebuilt. Document metadata. The merged file gets fresh document properties rather than inheriting the title and author of the first input, which is usually what you want when several authors are involved.

Mixed page sizes and print output

PDF allows every page in a document to have its own dimensions, so a merged file can hold A4 text pages next to a landscape spreadsheet and an A3 drawing. Readers handle this without complaint. Print shops sometimes do not, and courts often require a single page size across a bundle. If you need uniformity, standardise the pages with Crop PDF or re-export the odd document at the target size before merging.

When merging fails

• The file is rejected on load. Almost always encryption. A PDF with an owner or user password cannot be opened for editing. Save an unprotected copy first.
• The tab slows or stops. The job exceeded available memory. Merge in two passes, or compress the heaviest scans with Compress PDF before combining.
• The output is far larger than expected. Each source keeps its own embedded fonts and images, and duplicates across files are not deduplicated. A compression pass afterwards usually recovers a large share of it.

A note on sensitive bundles

Merging does not clean anything. If one of the input files carries hidden content, tracked changes converted to a layer, or author metadata you would rather not disclose, the merged document inherits it. For anything going to a regulator, an opponent, or a public filing, run Redact PDF or Flatten PDF on the sensitive parts before you combine, and open the final file once to confirm the result.