The Default Viewer
macOS comes with a built-in application called Preview, which is a surprisingly powerful tool for viewing images and basic PDF documents. Because it is an Apple-native app, macOS automatically sets Preview as the default handler for all PDF files. If you double-click a PDF on your desktop, it opens in Preview. However, if your workflow requires advanced PDF features—such as filling out complex cryptographic forms, utilizing specific digital signatures, or advanced color separations for print—Preview is often insufficient, and you will need to use a dedicated program like Adobe Acrobat Reader or PDF Expert.
Changing the Global Default
To streamline your workflow and stop macOS from automatically opening PDF files in the basic Preview app when you double-click them, you must change the default application association for the entire PDF file format.
First, find any PDF file on your Mac (on your Desktop or in your Documents folder). Do not double-click it. Instead, click it once to highlight it, then right-click (or Control-click) and select Get Info from the context menu. A long, narrow information panel will appear. Scroll down this panel until you find the section titled Open with:. Click the small arrow next to it to expand the section if it is hidden. Click the dropdown menu showing “Preview (default)” and select your preferred application, such as Adobe Acrobat Reader. Crucially, to make this change apply to all PDFs and not just this single file, you must click the Change All… button located just below the dropdown menu. Confirm your choice in the pop-up warning, and your Mac will now default to your professional software.