Adobe Acrobat Portfolio and Attachment Features Need Keyboard Accessibility Enabled to read documents and access the Open Document Link
Within Adobe Acrobat there are options to Create a Portfolio of documents or to use the Attachment feature to create a group of documents. While keyboard shortcuts allow you to browse some of the menus, get to the document list, and select a document from the list. However, there is not a keyboard short cut to read the document in the view or to access the Open Document link. It seems to be only available through mouse selection.
This places users of these features at risk because the end user can't access the document to read it using only keyboard selections. Since these features lack keyboard accessibility, the product is not fully accessible.
As I can see, the issue is related to keyboard keys, Please follow the below controls to access the Open Document link.
Use tab to click on Attachment in Left Hand Pane. Press tab multiple times to bring the focus on the Option menu. Click Enter and Use arrow keys to navigate inside Options menu items. This resolves your access to Open Document Link.
Secondly, Use Ctrl+Shift+Y and then Ctrl+Shift+V/B to read the document using Read out loud feature. You can alternatively see it in View Menu → Read Out Loud → Click Activate ROL → Click Read this page/ end of the document.
Please confirm if this resolves your issue.