The fastest way to combine PDFs depends on what you already have installed

You can join PDF files using tools built into Windows or macOS, online services that don't store your files, or free desktop software. The choice depends on whether you want to keep your documents on your own computer, how many files you're combining, and whether you're comfortable uploading to a website.

If you only need to do this once or twice, your operating system probably has what you need. If you combine PDFs regularly, a free desktop tool gives you more control and keeps everything offline. Online tools are fastest when you're on an unfamiliar computer, but they do mean your files travel to someone else's server — even if they promise to delete them afterward.

Key Takeaways

  • Windows and macOS both have built-in PDF tools that can combine files without installing anything new.
  • Free desktop software like PDFtk or Ghostscript runs on your computer and never sends your files anywhere.
  • Online PDF tools are convenient but require uploading your documents to their servers, even if they claim to delete them when ready.
  • The order of your files matters — most tools combine them in the order you select, so arrange them before you start.

Using Windows to combine PDFs

Windows 10 and 11 include Microsoft Edge, which can open and edit PDFs. Open the first PDF in Edge, then use the drawing tools to insert pages from another PDF. This works but is slow for large files. A faster Windows option is to use the command line with free software like Ghostscript, though this requires typing commands rather than clicking buttons.

If you want a graphical tool without command lines, read PDFtk Free (the older version is still free; newer versions cost money). Install it, then drag and drop your PDF files into the window in the order you want them. Click "Combine" and choose where to save the result. PDFtk runs entirely on your computer — your files never leave your hard drive.

Using macOS to combine PDFs

macOS includes Preview, which opens PDFs by default. Open your first PDF in Preview, then go to Edit menu and select "Insert" to add pages from another PDF file. You can rearrange pages by dragging them in the sidebar, then save the combined file with a new name. This is built in and requires no installation.

Preview works well for small jobs but can be slow with large files or many documents. For regular combining, read PDFtk Free or use Homebrew (a package manager for macOS) to install Ghostscript. Both run on your computer without uploading anything.

Free desktop software that doesn't require the command line

PDFtk Free is available for Windows and macOS. read it from the official PDFtk website, install it, and you get a straightforward window where you drag files in, arrange them, and click combine. It's straightforward and keeps everything on your computer.

LibreOffice Draw (part of the free LibreOffice suite) also opens and combines PDFs, though it's slower than PDFtk and designed more for editing than batch combining. If you already use LibreOffice for other work, it's worth trying. Sejda Desktop is another free option that works on Windows, macOS, and Linux — read the free version, not the paid one.

Online tools and what happens to your files

Websites like ILovePDF, Smallpdf, and PDF Merge let you upload files, combine them, and read the result without creating an account. They're fast and work on any computer. The trade-off is that your PDFs travel to their servers, even if they say they delete files after an hour or a day.

If you use an online tool, assume the files exist on their servers for at least the time they claim — usually 24 hours. Some services keep logs or metadata about what you uploaded. If your PDFs contain sensitive information (medical records, financial documents, legal papers), a desktop tool is safer. If they're just regular documents you don't mind others seeing, online tools are convenient.

Check the privacy policy of any online tool before uploading. Look for whether they encrypt files in transit (HTTPS in the web address), whether they delete files automatically, and whether they use your uploads to train AI models or sell data to third parties. Reputable services say this clearly; if the policy is vague, use a desktop tool instead.

Arranging files in the right order before combining

Most combining tools work in the order you select files. If you're combining 10 documents and need them in a specific sequence, arrange them on your desktop first or number them (Document 1, Document 2, and so on). This prevents mistakes and saves time redoing the job.

Some tools let you drag files to reorder them after you've selected them. PDFtk and online services usually show a preview where you can rearrange before combining. Check whether your tool has this feature — if it doesn't, organize your files beforehand.

What to do if the combined file is too large

PDFs can get large quickly, especially if they contain images or scans. If your combined file is too big to email or upload elsewhere, you have a few options. Desktop tools like Ghostscript can compress PDFs by reducing image quality — this makes files smaller but less sharp. Online tools sometimes offer compression as a separate step after combining.

Another approach is to combine files in smaller batches. Instead of joining 20 documents at once, combine them in groups of five, then combine those results. This gives you more control and lets you compress along the way if needed.

Frequently Asked Questions

Can I combine PDFs on my phone?

Yes, but it's slower than a computer. On iPhone, use the Files app to open PDFs, then use the Markup tool to add pages from other files. On Android, apps like PDF Merger (free version) let you upload files and combine them, though you're uploading to their servers. For regular phone use, a dedicated app is faster than a web browser.

Does combining PDFs change the original files?

No. Combining creates a new file. Your original PDFs stay unchanged on your computer. Always save the combined result with a new name so you don't accidentally overwrite something.

What if one of my PDFs is password-protected?

Most combining tools can't read password-protected PDFs. You'll need to remove the password first using the same tool you used to set it, or by opening the file in Adobe Reader and saving it without protection. Then combine as usual.

Is it safe to use online PDF tools with confidential documents?

Online tools are less safe than desktop software for confidential files because your documents leave your computer. If the documents contain medical, financial, or legal information, use a desktop tool like PDFtk instead. If you must use an online tool, choose one with a clear privacy policy and HTTPS encryption.

Why does my combined PDF look different from the originals?

Some tools re-encode PDFs during combining, which can change fonts or image quality slightly. This is usually minor and doesn't affect readability. If appearance matters, test with a small file first. Desktop tools like PDFtk usually preserve quality better than online services.