The basic steps for merging PDFs

Merging PDFs means taking two or more separate PDF files and combining them into a single document. The process itself is straightforward: you select the files you want to combine, arrange them in the order you want them to appear, and let the tool do the work. The result is one PDF file that contains all the pages from each original file, in sequence.

How you do this depends on which tool you use. Some tools let you drag and drop files directly into a window. Others ask you to browse your computer and select files one at a time. A few let you upload files from cloud storage like Google Drive or Dropbox. The end result is the same — one merged PDF — but the steps change based on the tool.

Key Takeaways

  • Desktop tools like PDFtk or ILovePDF let you merge files on your own computer without uploading anything to the internet.
  • Web-based tools like Smallpdf or PDF Merge require you to upload your files, which means your documents travel over the internet and sit on someone else's server temporarily.
  • The order matters — most tools let you drag pages or files to rearrange them before you finalize the merge.
  • Merged PDFs keep the original formatting and page numbers from each file, so you may need to renumber pages afterward if that matters for your use.
  • Some tools charge money for merging more than a few files per day or for removing their watermark from the output.

Desktop tools versus web-based tools

Desktop tools run on your computer. You read and install the software, then use it to open and merge your PDFs without sending them anywhere. Examples include PDFtk (free, command-line based), Preview on Mac (built in, drag-and-drop), and paid options like Adobe Acrobat Pro. The advantage is privacy — your files never leave your computer. The disadvantage is that you have to install software, and some desktop tools have a steeper learning curve.

Web-based tools live on the internet. You go to a website, upload your PDFs, and the tool merges them in your browser or on their server. Examples include Smallpdf, ILovePDF, PDF Merge, and Sejda. The advantage is simplicity — no installation, no learning curve, and you can use them from any device with a web browser. The disadvantage is that your files are uploaded to someone else's server, which raises privacy questions depending on how that company handles data.

If your PDFs contain sensitive information — tax documents, medical records, financial statements — a desktop tool keeps them off the internet entirely. If your PDFs are routine documents like meeting notes or public information, a web tool is usually faster and requires no setup.

How to merge PDFs on Mac using Preview

Mac computers come with Preview, a built-in tool that can merge PDFs without any additional software. Open Preview, then go to File > Open and select the first PDF you want to merge. Once that file is open, go to File > Open Again and select the second PDF. This opens the second file in a new Preview window.

In the first Preview window, go to View > Thumbnails to see all the pages as small images on the left side. Now switch to the second Preview window, select all its pages (Command + A), and copy them (Command + C). Go back to the first window, click after the last page in the thumbnail panel, and paste (Command + V). The pages from the second file now appear at the end of the first file. Repeat this for any additional PDFs you want to add. When you are done, go to File > Export As, choose PDF as the format, and save your merged file.

How to merge PDFs using a web-based tool

Web-based tools follow a similar pattern regardless of which one you choose. Go to the website (Smallpdf, ILovePDF, or PDF Merge are common options). Look for a button that says "Select Files" or "Upload Files" or shows a box where you can drag files. Click that button and browse your computer to find the first PDF, or drag the file directly into the box.

Once the first file uploads, the tool usually shows you a preview and asks if you want to add more files. Click the button to add another file and repeat the process. Most tools let you see all your files listed and let you drag them to reorder them before you merge. When the order is correct, click a button like "Merge" or "Combine" and wait for the tool to process the files. This usually takes a few seconds to a minute depending on file size and how busy the service is.

When the merge is complete, the tool gives you a read button. Click it to save the merged PDF to your computer. Some tools automatically delete your files after a few hours; others let you delete them manually. Check the tool's privacy page if you want to know exactly when files are removed from their servers.

Reordering pages before you merge

Most tools let you change the order of your files or pages before the merge happens. In web-based tools, this usually means dragging files up or down in a list, or dragging thumbnail images to new positions. In desktop tools like Preview, you can rearrange pages in the thumbnail panel by dragging them to a new spot.

This matters because the merged PDF will contain pages in the exact order you arrange them. If you want pages 1–5 from File A, then pages 1–3 from File B, then pages 6–10 from File A, you need to set that up before you merge. Some tools let you do this by merging files in a specific order and then rearranging the result. Others require you to extract specific pages from each file first, then merge those extracted files in the order you want.

What happens to page numbers and formatting

When you merge PDFs, each original file keeps its own page numbering. If File A has pages 1–10 and File B has pages 1–8, the merged PDF will have pages 1–10 from File A followed by pages 1–8 from File B. The page numbers do not automatically renumber to 1–18. If you need continuous page numbering across the entire merged document, you will need to use a more advanced tool like Adobe Acrobat Pro or PDFtk, or manually edit the page numbers after merging.

Formatting — fonts, colors, images, layout — stays exactly as it was in the original files. Merging does not change how the content looks. However, if the original PDFs have different page sizes (one is letter-size, another is legal-size), the merged PDF will contain both sizes. Some tools let you standardize page size before merging, but most do not.

Free versus paid tools and their limits

Most web-based PDF tools offer a free version with limits. Common limits include merging only a few files per day, a maximum file size (often 25 MB or 50 MB per file), or a watermark added to the output. Paid versions remove these limits and sometimes add features like batch processing (merging many files at once) or advanced editing.

Desktop tools vary widely. Preview on Mac is free and unlimited. PDFtk is free but requires command-line knowledge. Adobe Acrobat Pro costs money but offers extensive PDF editing beyond just merging. If you only merge PDFs occasionally, a free web tool is usually sufficient. If you merge files regularly or need to process large batches, a paid tool or a desktop tool may save you time.

Frequently Asked Questions

Can I merge PDFs on my phone?

Yes, but it is more limited than on a computer. Apps like Adobe Acrobat Reader (free version), PDF Merge, and Smallpdf have mobile versions that let you select files and merge them. The process is slower and works better for small files. For regular or large-scale merging, a computer is more practical.

What if the PDFs are password-protected?

Most tools cannot merge password-protected PDFs without you removing the password first. You will need to open each PDF with its password, save it as an unprotected copy, and then merge those copies. Some paid tools like Adobe Acrobat Pro can handle protected files directly if you have the password.

Does merging change the file size?

The merged PDF is usually slightly larger than the sum of the original files because the tool adds some overhead. The increase is usually small — a few kilobytes — but it depends on the tool and the complexity of the PDFs. Highly compressed PDFs may stay about the same size when merged.

Can I undo a merge after I save it?

No. Once you save the merged PDF, you cannot undo the merge using the tool that created it. You would need to go back to the original files and start over. Always keep your original PDFs in case you need to merge them differently later.

What if I only want to merge specific pages from each file?

Most basic merge tools combine entire files. To merge only certain pages, you first need to extract those pages into separate PDFs using a tool like Preview, Adobe Acrobat, or an online page extractor. Then merge the extracted files. Some advanced tools like PDFtk let you specify page ranges directly in the command, but this requires technical knowledge.