Merging PDFs is one of the most common document tasks — invoices into one file for an expense report, contracts and exhibits into a single review packet, scanned pages into a single PDF to email. The task is simple, but the tools are not all equal.
This guide covers:
- What merging does — and what it doesn't.
- The fastest free methods on Mac, Windows, and the web.
- How to keep page order, bookmarks, and text searchable.
- Common pitfalls — encrypted PDFs, huge scans, and page-size mismatches.
What merging does
A merge takes two or more PDF files and concatenates their pages in order into one new PDF. The output is a single file whose page 1 is the first page of the first input, and whose last page is the last page of the last input.
What it does NOT do:
- It does not "combine" text across files. Each page's content is preserved as-is. If page 3 of file A is a table and page 1 of file B is a paragraph, the merged PDF has both, unchanged.
- It does not merge bookmarks by default. Most tools drop the outline (table of contents) unless you specifically ask for it.
- It does not merge form fields. If both files have fillable forms, the merged file will have both forms' fields — sometimes overlapping.
Fastest free methods
macOS — Preview
- Open the first PDF in Preview.
- View → Thumbnails to show the sidebar.
- Drag the second PDF's thumbnail into the sidebar at the position where you want its pages to appear.
- File → Export as PDF to save the merged file.
Preview also lets you drag individual pages between files. The sidebar is the workspace.
Windows — Edge or a free web tool
Microsoft Edge opens PDFs natively but doesn't merge them. The simplest Windows-native path is to use a web tool (see below) or install a free tool like PDF24 or PDFsam Basic.
Web — DocShop
DocShop's merge tool runs the merge in your browser. Drop the files in the order you want, drag to reorder if needed, and the output PDF downloads. The upload and result are deleted within an hour — see How we handle your files for the full timeline.
Why browser-side matters for merging: merging is the most common tool for confidential documents (contract packets, medical records, financial statements). Running it in the browser means the file never leaves your machine.
Linux — PDFsam or pdftk
pdftk is the classic command-line tool:
``
pdftk A=file1.pdf B=file2.pdf cat A B output merged.pdf
``
Order of A B on the cat line is the order in the output. Swap to B A for the reverse.
Keeping page order, bookmarks, and text searchable
Page order
Most tools preserve input order. To reorder, either:
- Name the files with numeric prefixes (01-cover.pdf, 02-body.pdf, 03-appendix.pdf) and merge alphabetically.
- Use a tool that lets you drag-and-drop to reorder (Preview, DocShop, PDFsam).
Bookmarks
- Preview: drops bookmarks. If the outline matters, use PDFsam or Acrobat.
- PDFsam: option to "merge outlines" in the merge dialog.
- DocShop: preserves the first file's outline; subsequent files' outlines are dropped (the merged file's structure is page-order, not bookmark tree).
Text searchability
A merged PDF is text-searchable if and only if every input was text-searchable. A scanned image PDF merged with a digital PDF produces a merged PDF where only the digital pages are searchable. To fix, OCR the scanned files before merging (see "How to OCR a PDF without Adobe").
Common pitfalls
- Encrypted PDFs. Merging an encrypted PDF usually fails or produces an encrypted output. Unlock the PDF first (or use a tool that prompts for the password).
- Huge scans. Merging 10 × 20MB scanned PDFs produces a 200MB file. Compress first (see "How to compress a PDF for email attachment").
- Mixed page sizes. Letter + A4 + legal in one merge produces a file where each page keeps its original size. This is usually what you want; if you need uniform sizing, standardize before merging.
- Bookmark drop. If the output has no table of contents, the tool dropped it. Check the tool's merge options for "preserve outlines."
Privacy
Merging is where the confidentiality question matters most — contract packets, medical records, financial filings. DocShop runs the merge in an isolated container, deletes the upload and result within an hour, and never reads the content. The full timeline is at How we handle your files.
Prefer a local tool (Preview, PDFsam, pdftk) when the document is privileged or under NDA — the file never leaves your machine.