Merging PDFs, stitching a scanned contract to its cover letter, or bundling several reports into one file, is a common task with a different answer depending on your computer. A Mac has a capable tool built in; Windows does not, so you choose between an online service and a free desktop program. All the routes below are free, and the right one mostly depends on how private your documents are.

Merge PDFs on a Mac with Preview

Preview, the viewer that opens PDFs by default on a Mac, can combine files entirely offline, so nothing leaves your computer. Because Preview edits the file directly as you work, it is worth duplicating the first PDF before you start.

  1. Open the first PDF. If it does not open in Preview, right-click the file and choose Open With > Preview.
  2. To keep the original intact, click File > Duplicate and work on the copy.
  3. Show the thumbnail sidebar with View > Thumbnails, or press Option + Command + 2.
  4. Open a Finder window, find the second PDF, and drag it into the thumbnail sidebar. A thin grey line shows exactly where the pages will be inserted, so drop it after the page you want.
  5. Repeat for any other PDFs. You can drag individual thumbnails up or down to reorder pages.
  6. Save the combined file with File > Export as PDF, give it a name and choose a location.

Preview can also pull single pages from one PDF into another the same way, which is handy when you only need a page or two rather than the whole document.

Merge PDFs online (Windows or Mac)

The quickest cross-platform option is a browser-based merger such as Adobe’s free online tool, Smallpdf or iLovePDF. They work the same way: you upload the files, drag them into the order you want, and download the single merged PDF. Adobe’s basic merge needs no software installed and no paid subscription, and it does not stamp a watermark on the result.

  1. Open the merge tool in your web browser.
  2. Click to add or drag in the PDF files you want to combine.
  3. Drag the file thumbnails to set the order.
  4. Click Merge or Combine, then download the finished PDF.

The trade-off is that your files are uploaded to someone else’s servers to be processed. Reputable services delete them after a short period, but you should still avoid online tools for anything confidential, such as financial records, medical documents or signed contracts. Free tiers may also cap the file size or the number of files per merge.

Merge PDFs offline on Windows

Windows 10 and 11 have no drag-and-drop PDF merger built in, so for private files you want a free desktop program that keeps everything on your machine.

  • PDFsam Basic is free and open-source, with a straightforward Merge module: add your files, arrange the order, and run the merge. It is a popular choice precisely because it works entirely offline.
  • PDFtk (PDF Toolkit) is a free command-line tool for people comfortable typing a command to combine files.
  • If you installed the paid Adobe Acrobat (not the free Reader), it has a built-in Combine Files feature as well.

The Microsoft Print to PDF workaround

There is a manual trick that needs no extra software, though it only works well for a couple of short files. Open the first PDF, choose Print, and pick Microsoft Print to PDF as the printer. This method is fiddly for combining whole documents because you cannot easily merge several multi-page files in one step, so most people are better off with PDFsam for anything beyond the simplest job.

Merge PDFs on a phone

If the files live on your phone, the same online services have apps, and the Adobe Acrobat and iLovePDF apps can combine PDFs on both iPhone and Android. On an iPhone you can also open a PDF in the Files app, tap and hold, and use the share or edit options, though a dedicated PDF app is usually smoother for reordering pages.

Check the result before you delete the originals

Whatever tool you use, open the merged PDF and scroll through it once before throwing away the source files. Confirm that every page is present, that the order is right, and that nothing was rotated or cropped during the merge. Pay particular attention to the seams where one document joins the next, since a missing or duplicated page is easiest to miss there. If the files contained fillable form fields, digital signatures or bookmarks, check that those survived, because some merge tools flatten forms into plain pages or drop signatures. When a signature or form must stay interactive, a dedicated PDF editor such as Acrobat handles it more reliably than a quick online merge.

Keeping merged files a sensible size

Combining several image-heavy PDFs can produce a file too large to email. If that happens, most online tools and desktop apps offer a separate Compress option you can run on the finished document to shrink it. On a Mac, Preview’s Export dialog includes a Quartz Filter called Reduce File Size that does the same job in one step. Compress a copy rather than your only version, as aggressive compression can soften scanned text, and compare the two before you commit.

Choosing the right method

The decision comes down to two questions: what computer are you on, and how sensitive are the files? On a Mac, Preview handles almost everything for free and offline, so start there. On Windows, reach for an online tool when the documents are not confidential and speed matters, or PDFsam Basic when privacy does. Whatever route you pick, set the page order before you save, and keep a copy of the original files until you have confirmed the merged PDF looks right.

Merging scanned pages into one document

A frequent reason to merge is to turn a stack of single-page scans into one document, for instance when a scanner saves each page separately. The process is identical: load the pages in order and combine them. If the pages came out in the wrong sequence, use the thumbnail view in Preview or the reordering screen in your chosen tool to drag them into place before saving. When you scan directly on a phone, the Notes app on iPhone and many scanner apps on Android already produce a single multi-page PDF, which saves you merging them afterward. If you only have photos of documents rather than true scans, convert them to PDF first, then merge, so the final file opens cleanly on any device.

Quick recap

Mac users should drag files into Preview’s thumbnail sidebar and export. Windows users have no native merger, so pick a trusted online service for everyday files or an offline app like PDFsam Basic for private ones. Either way the core steps are the same: add the files, arrange the order, check the result, and save the single combined PDF.