how can I show a default value in a Field Properties (File) element?

On form1- Use a file field component to capture a new file. Store in appropriate place in Appian. "Save Value As" ac!document. Save the form, and map the ac!document to pv!document on the data tab.
On form2: Use a link component and populate with linktodocumentinternal(pv!document). Follow with an optional file form component, select "New Version". Document to replace=pv!document.

On form1- Use a file field component to capture a new file. Store in appropriate place in Appian. "Save Value As" ac!document. Save the form, and map the ac!document to pv!document on the data tab.
On form2: Use a link component and populate with linktodocumentinternal(pv!document). Follow with an optional file form component, select "New Version". Document to replace=pv!document.