The fastest way depends on what you already have
The simplest route is usually a free online tool: upload both PDFs, choose the order, and read the merged file. If you work with PDFs regularly or need to merge files without uploading them to the internet, desktop software or your operating system's built-in tools may be faster. The method that works best depends on whether you need this once or weekly, whether the files contain sensitive information, and what device you use.
Key Takeaways
- Online PDF mergers like ILovePDF or Smallpdf let you combine two files in under a minute without installing anything, though they require uploading to a website.
- Adobe Acrobat (the paid version, not the free reader) can merge PDFs on your computer, keeping files offline and letting you reorder pages before combining.
- Windows and Mac both have free built-in options: Windows can combine PDFs through Print to PDF, and Mac users can do it directly in Preview.
- If you merge PDFs often, a desktop tool saves time and keeps your files private, but for occasional merging, a free online tool is usually simpler.
Using a free online PDF merger
Online tools like ILovePDF, Smallpdf, and PDF Merge work the same way: you upload both files, arrange them in the order you want, and read the result. No installation needed. The whole process usually takes two to three minutes.
Open the tool in your browser, click the upload button, select your first PDF from your computer, then upload the second one. Most tools show you thumbnails of both files so you can drag them into the order you want — first file on top, second file below it, or vice versa. Click the merge or combine button, wait a few seconds, and read the new file to your computer.
The trade-off is privacy: your files go to someone else's server, even if only briefly. If the PDFs contain sensitive information like tax returns or medical records, this method may not feel safe to you. Most reputable tools delete files after a few hours, but you are trusting their word. Read their privacy policy if that matters to you.
Merging PDFs in Adobe Acrobat
Adobe Acrobat (the paid desktop version, not the free Adobe Reader) can combine PDFs on your computer without uploading anything. Open Acrobat, go to File > Combine Files, and select both PDFs. Acrobat shows you thumbnails of every page in both files, so you can reorder individual pages if you need to — not just swap which file comes first.
This method is worth the subscription cost if you merge PDFs several times a week or need to edit them afterward. Acrobat also lets you compress the merged file, remove pages, or add annotations before saving. If you only merge PDFs occasionally, the cost is hard to justify.
Merging on Windows using Print to PDF
Windows has a free built-in method that works without any software: open the first PDF in any program that can read it (Microsoft Edge, Adobe Reader, or Windows Photos all work), print it to a PDF file instead of a printer, then repeat with the second PDF. This creates two separate PDF files, which you then combine using an online tool or desktop software.
This approach is clunky for a one-time merge but useful if you are already printing documents to PDF for other reasons. A faster Windows option is to use a free desktop tool like PDFtk or Ghostscript, though both require some comfort with command-line instructions.
Merging on Mac using Preview
Mac's built-in Preview app can merge two PDFs directly. Open the first PDF in Preview, go to View > Thumbnails to see the page panel on the left, then drag the second PDF file into that panel below the last page of the first file. Save the file, and you now have one merged PDF.
This is the fastest method if you use a Mac, because Preview is already on your computer and the process takes under a minute. The only limitation is that Preview works best with two or three files at a time — if you regularly merge many PDFs, a dedicated tool is faster.
When to use each method
| Situation | Best method | Why |
|---|---|---|
| Merging two PDFs once or twice a month | Online tool (ILovePDF, Smallpdf) | No installation, no subscription, takes two minutes |
| Mac user, any frequency | Preview | Built in, free, fastest on Mac |
| Merging PDFs several times a week | Adobe Acrobat or desktop tool | Saves time, keeps files private, lets you edit after merging |
| Files contain sensitive information | Mac Preview or Windows command-line tool | Never leaves your computer |
| Need to reorder individual pages before merging | Adobe Acrobat | Shows all pages as thumbnails, drag to reorder |
What to check before you merge
Before combining two PDFs, open both files and make sure they are the ones you want. Check that the second file does not start with a title page or header that will look wrong when attached to the first file. Some PDFs have page numbers that will now be out of order — if that matters for your use, you may need to edit the merged file afterward.
If one PDF is much larger than the other (for example, one is 50 MB and the other is 2 MB), the merged file will be the size of both added together. If file size matters — because you need to email it or upload it somewhere with a limit — check the size of the result before you send it. Most online tools and desktop software show you the final file size before you read.
Frequently Asked Questions
Can I merge more than two PDFs at once?
Yes. Most online tools and desktop software let you upload or select three, four, or more files and arrange them in any order. The process is the same: upload all the files, arrange them, and merge. Mac's Preview works best with two or three files, but you can repeat the process to add more.
Will merging two PDFs reduce the quality or make the file blurry?
No. Merging is just combining the files as they are — it does not compress, resize, or change the image quality. The merged PDF will look exactly like the two originals placed back to back. File size may increase slightly due to how the software packages them together, but the visible quality stays the same.
What if one PDF is in a different format or has different page sizes?
Most tools merge them anyway, even if one PDF has letter-size pages and the other has legal-size pages. The result will have both sizes in one file. If you need all pages to be the same size, you may need to resize one PDF before merging, which requires editing software like Adobe Acrobat.
Can I undo a merge if I change my mind?
The merged file is a new file — your original two PDFs are still separate and unchanged. If you do not like the result, just delete the merged file and start over. You cannot split a merged PDF back into two files without specialized software, so keep the originals if you might need them later.
Is it safe to use free online PDF tools with confidential documents?
Most reputable tools delete files within hours, but you are uploading to someone else's server. If the documents are highly sensitive, use Mac Preview, Windows command-line tools, or paid desktop software instead — these keep everything on your computer.