Portfolio PDFs can only be opened with Adobe Acrobat. If you attempt to open the file with your browser's PDF reader you'll be prompted to download Acrobat to open the file.
If a portfolio PDF has been shared with you in OneDrive, and you click to open the file, your browser will try to display the PDF in a new tab. Instead of seeing the PDF you'll see what is in the image below:
(Note: The screenshots below are using the Chrome browser on Windows 10. Things may look slightly different if you're using a different browser, or macOS, but the process is similar.)
Hover your mouse cursor over the window, and contextual icons will appear. In the upper right corner is a download button. Click the download button to save the file to your computer.
A Save As dialog box will appear. Choose the location, and name the file appropriately. Click Save.
Once the file has saved the downloaded file will appear at the bottom of your window. Click the downward facing caret ( v ), next to the downloaded file, then click Show in folder.
The File Explorer window will appear. Right-click the saved PDF, click Open with, then click Adobe Acrobat Reader DC (or Adobe Acrobat DC).
If you don't have Adobe Acrobat Reader DC or Adobe Acrobat DC to choose from, you will need to first install it from Software Center, or Manager before you can open the portfolio PDF.