Workbook Properties

Unlike Word, there is no concept of Workbook Variables, only Workbook Properties.

Workbook Built-in Properties

ActiveWorkbook.BuiltinDocumentProperties.Item("Subject") 
ActiveWorkbook.BuiltinDocumentProperties("Subject") 
ActiveWorkbook.BuiltinDocumentProperties.Item(2) 
ActiveWorkbook.BuiltinDocumentProperties(2) 

This returns a collection that represents all the built-in document properties for the specified workbook.
You can refer to built-in document properties either by index value (1 based) or by name.
The following list shows the available built-in document property names.
There is no enumeration like there is in Word.

Workbook Custom Properties

objDocument.CustomDocumentProperties 

Public Sub DocumentProperties() 
Dim icount As Integer 
Dim objDocumentProperty As DocumentProperty 

   For icount = 1 To ActiveWorkbook.BuiltinDocumentProperties.Count 
      Set objDocumentProperty = ActiveWorkbook.BuiltinDocumentProperties.Item(icount) 

      Debug.Print objDocumentProperty.Name 
      Debug.Print objDocumentProperty.LinkSource 
      Debug.Print objDocumentProperty.LinkToContent 
      Debug.Print objDocumentProperty.Parent 
      Debug.Print objDocumentProperty.Type 
      Debug.Print objDocumentProperty.Value 
   Next icount 
End Sub 

Name - Specifies the property name
Type - The type of the property
Value - This is current setting

With the properties LinkSource and LinkToContent the value of a custom property can be linked directly to the contents of a worksheets
LinkSource - Gets or sets the source of a linked custom document property. The LinkToContent the value of a custom property can be linked directly to the contents of a worksheets
LinkToContent - Is True if the value of the custom document property is linked to the content of the container document. False if the value is static. This must be set to True and LinkSource must be a named range to the cell.

Workbook Custom Properties

ActiveWorkbook.CustomDocumentProperties 

This property returns the entire collection of custom document properties.
You can only refer to the custom document properties by their name. You cannot use a 1-based index value.
Use the Item method to return a single member of the collection (a DocumentProperty object) by specifying either the name of the property or the collection index (as a number).

CustomDocumentProperties.Item("BetterSolutions") 
CustomDocumentProperties("BetterSolutions") 

msoPropertyTypeString

This will extract all the custom properties from a workbook

Public Sub CustomProperties_Extract() 
Dim icount As Integer 
Dim objDocumentProperty As DocumentProperty 
   For icount = 1 To ActiveWorkbook.CustomDocumentProperties.Count 
      Set objDocumentProperty = ActiveWorkbook.CustomDocumentProperties.Item(icount) 
      ThisWorkbook.Worksheets("Sheet1").Range("A" & icount).Value = objDocumentProperty.Name 
      ThisWorkbook.Worksheets("Sheet1").Range("B" & icount).Value = objDocumentProperty.Value 
      ThisWorkbook.Worksheets("Sheet1").Range("C" & icount).Value = objDocumentProperty.Type 
   Next icount 
End Sub 

This will import a list of custom properties into a workbook

Public Sub CustomProperties_Import() 
Dim lrowlast As Long 
Dim lrowno As Long 
   lrowlast = ThisWorkbook.Worksheets("Sheet1").Range("A1").SpecialCells(xlLastCell).Row 
   For lrowno = 1 To lrowlast 
      Call Workbooks("ISP.xlsx").CustomDocumentProperties.Add( _ 
         Name:=ThisWorkbook.Worksheets("Sheet1").Range("A" & lrowno).Value, _ 
         LinkToContent:=Office.MsoTriState.msoFalse, _ 
         Value:=ThisWorkbook.Worksheets("Sheet1").Range("B" & lrowno).Value, _ 
         Type:=Office.MsoDocProperties.msoPropertyTypeString) 
   Next lrowno 
End Sub