PDF Reader Pro for Mac has several ways to open PDFs:
1. Make PDF Reader Pro your default viewer. Tap PDF Reader Pro -> Preferences..., and tick Set PDF Reader Pro as the default PDF viewer. If you set it as your default app for opening PDFs, double-click on a PDF file in Finder, and it will be opened in PDF Reader Pro.
2. Drag and drop. On a New tab screen drag-n-drop any PDF file from Finder to the highlighted area.
3. Open directly. On a New tab screen press Select file... and choose a document from the file selection window.
4. Drag to the Dock icon. When PDF Reader Pro is in your dock, just drag-n-drop PDF file on the PDF Reader Pro icon, and the file will be opened in a new tab.