The fastest way to merge PDFs depends on what you have on hand

If you have Adobe Acrobat (the paid version, not the free Reader), you can merge PDFs directly: open Acrobat, go to File > Combine Files, select the PDFs in the order you want them, and click Combine. The result is a single PDF with all pages in sequence.

If you don't have Acrobat, your operating system likely has a built-in tool. On Mac, you can drag multiple PDFs into Preview, arrange them in the sidebar, then export as a single PDF. On Windows 10 and 11, Microsoft Print to PDF lets you print multiple documents to one file. For anything else — or if you want more control over page order — free online tools like ILovePDF, Smallpdf, or PDFtk work in a browser without installing software.

The trade-off is simple: desktop software is faster for large batches, but online tools are easier if you're merging just two or three files and don't want to install anything.

Key Takeaways

  • Adobe Acrobat's Combine Files feature is the fastest method if you already own it, and lets you reorder pages before merging.
  • Mac's Preview and Windows 11's Print to PDF are free built-in options that work without downloading extra software.
  • Free online tools like ILovePDF or Smallpdf work in any browser and let you upload, arrange, and download a merged PDF in minutes.
  • The order you add files matters — most tools merge them in the sequence you select, so arrange them before you start.
  • Some tools compress the final PDF to reduce file size, which can make text slightly blurry; check the settings if quality matters.

Using Adobe Acrobat on Windows or Mac

Open Adobe Acrobat (not Adobe Reader — Reader cannot merge files). Click File in the top menu, then select Combine Files. A window opens where you can add PDFs one at a time or select multiple files at once by holding Ctrl (Windows) or Command (Mac) while clicking.

Once all files are added, you'll see them listed in order in the Combine Files window. Drag any file up or down to reorder before merging. Click Combine Files at the bottom right. Acrobat creates a new PDF with all pages in the order you set, then asks where to save it. This method is reliable and gives you full control, but requires an Acrobat subscription (around $20 per month or $240 per year).

Merging PDFs on Mac using Preview

Open the first PDF in Preview (the default PDF viewer on Mac). Go to File > Open and select the other PDFs you want to merge while holding Command. They'll open as separate tabs in Preview. Click View in the top menu and select Thumbnails to see a sidebar with page thumbnails from the active document.

Now drag the thumbnail pages from the other open PDFs into the sidebar of your main document. You can drag entire pages or groups of pages, and arrange them by dragging within the sidebar. Once all pages are in the right order, go to File > Export As, choose PDF from the format dropdown, name your file, and save. Preview merges everything into a single PDF without any quality loss.

Merging PDFs on Windows using Print to PDF

Open the first PDF in any PDF reader (Edge, Adobe Reader, or your default viewer). Go to File > Print. In the printer dropdown, select Microsoft Print to PDF. Click Print, choose where to save the file, and name it — this creates a PDF of the first document.

Repeat for each additional PDF you want to merge, but this time print to a file with a temporary name (like "temp2.pdf"). Once you have all the individual PDFs, use an online tool or desktop software to combine them in the correct order. This method is slower than the others because you're creating separate files first, but it works on any Windows version without extra software.

Using free online tools like ILovePDF or Smallpdf

Go to ILovePDF.com or Smallpdf.com in your browser. Look for a "Merge PDF" or "Combine PDF" button on the homepage. Click it, then click the upload area and select all the PDFs you want to merge from your computer. Most tools let you select multiple files at once.

Once uploaded, you'll see thumbnails of each PDF. Drag them to reorder if needed — the tool merges them in the order shown. Click Merge or Combine, wait a few seconds, then download the result. The entire process takes about two minutes. These tools are free for basic use, though they may compress the file slightly to reduce size. If you need to merge large files or do this frequently, both sites offer paid plans without compression.

What happens to file size and quality when you merge

When you merge PDFs, the file size is usually the sum of all the original files combined. If you merge a 5 MB PDF with a 3 MB PDF, expect roughly an 8 MB result. Some online tools compress the final file to make it smaller, which can make text slightly less sharp — this is a trade-off you control in the tool's settings.

Desktop methods (Acrobat, Preview, Print to PDF) typically preserve quality because they don't compress. If the merged PDF will be printed or needs to be very clear, use a desktop method. If it's just for email or sharing on screen, online tools are fine and the file size savings can matter.

Handling PDFs with different page sizes or orientations

If you're merging a portrait PDF (taller than wide) with a landscape PDF (wider than tall), most tools keep each page in its original orientation. The result is a PDF where some pages are portrait and some are landscape — this is usually fine for reading on screen, but can look odd when printed.

If you need all pages in the same orientation, you'll need to rotate pages before merging. In Adobe Acrobat, right-click a page thumbnail and select Rotate. In Preview on Mac, select a page thumbnail, go to Tools > Rotate, and choose the direction. After rotating, merge as normal. Online tools usually don't offer rotation, so do this step in desktop software first.

Frequently Asked Questions

Can I merge PDFs on my phone or tablet?

Yes, using online tools. Open ILovePDF or Smallpdf in your phone's browser, tap Merge PDF, and upload files from your device's storage. The process is the same as on a computer. Some phones also have built-in PDF apps — check your device's app store for "PDF merger" to see if a free app is available for your phone.

What if the PDFs are password-protected?

You'll need to unlock them first. If you know the password, open each PDF in your reader, enter the password, and save an unlocked copy. Then merge the unlocked versions. Most tools cannot merge password-protected files directly because they can't read the content.

Does merging PDFs change the original files?

No. Merging creates a new PDF file. Your original files stay exactly as they were. You can safely merge the same PDF multiple times or into different combined files without affecting the original.

Why is my merged PDF so large?

Each page from each original PDF is included in full, so the merged file is roughly the sum of all original file sizes. If file size is a problem, use an online tool's compression option, or compress the merged PDF afterward using a tool like Smallpdf's Compress PDF feature.

Can I merge PDFs and remove some pages at the same time?

Most merge tools don't let you delete pages during the merge. Instead, open each PDF in Adobe Acrobat or Preview, delete the pages you don't want, save the edited version, then merge. This takes a few extra minutes but gives you full control over what ends up in the final file.