How do I combine multiple PDFs into one PDF on mac?

The simplest and safest method on a Mac is usually Preview, which is already included with macOS.

1. Make a copy of the original PDFs first, because Preview may save changes automatically.
2. Open the first PDF in Preview.
3. Select View > Thumbnails to display the page sidebar.
4. Open the other PDF in another Preview window.
5. Drag its page thumbnails into the sidebar of the first PDF.
6. Rearrange the pages by dragging them into the correct order.
7. Select File > Export as PDF and save the combined document under a new filename.

This normally preserves the original page appearance and quality because the existing PDF pages are being combined rather than printed or converted into images. Apple officially supports merging complete PDFs or individual pages this way. 

For occasional merging, Preview is probably all you need. If you frequently manage large documents or want a more guided interface, Adobe Acrobat also has a dedicated Combine Files feature, but its desktop editing tools generally require a paid plan. 

A free PDF editor such as PDFgear is another practical option when you want to add several files, rearrange them visually, and merge them without learning Preview’s drag-and-drop workflow. For simply combining PDFs, a free editor is usually sufficient, so there is little reason to pay for Acrobat unless you also need advanced document editing or business features. 

Avoid online merging tools for confidential documents, since the files may need to be uploaded to a third-party server. After merging, check the page order, links, bookmarks, forms, and signatures before deleting the originals.