How to merge PDF files into one, step by step

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You have a contract in three parts, a set of receipts, or a CV plus a cover letter, and the recipient wants one file. Here is how to join PDFs in your browser, what to check first, and what your Mac or Microsoft 365 account can do instead.

Before you start

Three minutes of preparation saves a redo:

1. Collect the files in one folder and give them names that sort sensibly (01, 02, 03).
2. Check for passwords. If a PDF asks for a password to open, the merge tool cannot read it. Remove the protection in the program that created it, if you are allowed to.
3. Check the size. ConvertMango accepts up to 30 PDFs and 50 MB in total per merge. If the combined inputs exceed 50 MB, merging them in smaller batches may still leave final inputs above the limit. Reduce the files' size, keep separate outputs, or use a tool with a higher limit.

Step by step with Merge PDF

1. Open Merge PDF.
2. Add your PDFs, either by choosing files or by dragging them in.
3. Look at the list. Files are merged in exactly the order shown.
4. Use the up and down buttons to put them in the order you want. The first file in the list supplies the first pages of the result.
5. Press the merge button.
6. Download the result. The file is named convertmango-merge-pdf.pdf; rename it to something meaningful straight away.
7. Open it and scroll through. Check the page count (add up the originals), the order, and the first and last page of each part.

The merge runs in your browser, so the file contents are not uploaded to ConvertMango's conversion service. You get five free conversions a day without signing up, and the allowance resets at 00:00 UTC. A conversion only counts when it succeeds.

Convert it now: Merge PDF.

Getting the order right

The most common mistake is not a technical one: the files go in alphabetical order and "Appendix" lands before "Introduction". A few habits help:

• Number the files before you start.
• If one document should go in the middle of another, use Extract PDF pages to save the part before and the part after the insertion point as separate PDFs, then merge the pieces in the order you need.
• Keep the originals. The merge makes a new file and leaves yours as they were.

Naming the result

Give the merged file a name that says what it is and when it was made, for example the project, the version and the date. Generic names such as the default output name are easy to confuse with earlier attempts when you merge more than once.

Counting pages

Add up the pages of each source and compare with the merged file. If the totals differ, one file probably failed to load or was added twice. Scanned documents are a frequent source of surprise because a "single" scan may already hold several pages.

What if you have pictures, not PDFs?

Turn them into a PDF first with JPG to PDF, which can size each page to its image or place images on A4 portrait pages, then merge that PDF with the others. If the final file seems stuck at the wrong page size, that is where to look. See What is a PDF for how PDF treats pages.

On a Mac: Preview

Apple's Preview guide describes this route:

1. Open the PDFs in Preview.
2. In each, choose View > Thumbnails to show the page thumbnails in the sidebar.
3. Drag thumbnails from one PDF's sidebar into the other. Hold Command to select pages that are not next to each other.
4. To add a whole PDF, drag its icon from the Finder into the sidebar of an open document.
5. To reorder pages, drag thumbnails within the sidebar.

Apple's warning is worth repeating: Preview saves changes automatically, so use File > Duplicate on each PDF first if you want to keep the originals.

On Windows and Microsoft 365

Microsoft's documentation covers one route: Merge in OneDrive or SharePoint. You open one of the PDFs, choose More options (...), then Merge, select the other files, and save the combined file. Microsoft states the feature is available for users with a per-user or pay-as-you-go licence, or with SharePoint in their subscription plan, so it depends on your account. This guide does not describe other Windows routes, because only the OneDrive and SharePoint one is covered in Microsoft's documentation we checked.

Limits worth knowing

Merging joins pages as they are. It does not compress, repair or edit them, and it will not fix a PDF that is already damaged. Signatures, bookmarks, form fields and similar features inside the originals may not behave as they did separately, and we do not promise they are preserved, so check the result if you rely on them.

Common problems

• The merge tool rejects a file. It is most likely password-protected, damaged, or too large for the 50 MB total.
• Pages look the wrong size. The source files had different page sizes. Merging joins pages as they are and does not resize them.
• The file is too big to email. Merge fewer or smaller documents, or send two files rather than one.
• A page is missing. Check the original: it may have been missing before the merge.

After merging

If a section is no longer needed, Extract PDF pages can save selected pages as a new PDF. For the background on the format itself, read What is a PDF.

Frequently asked questions

Related tools

More guides

Sources

Plain-text references. Facts that could not be checked against a primary source were left out.

1. Apple, 'Combine PDFs in Preview on Mac', https://support.apple.com/guide/preview/combine-pdfs-prvw43696/mac
2. Microsoft, 'Merge and extract PDF files', https://learn.microsoft.com/en-us/microsoft-365/documentprocessing/merge-extract-pdf?view=o365-worldwide
3. Library of Congress, 'PDF (Portable Document Format) family', https://www.loc.gov/preservation/digital/formats/fdd/fdd000030.shtml