【VBA】ブックの存在確認｜fso（FileSystemObject）を使う

Public Function BookExists(ByVal fullPath As String) As Boolean
    Dim fso As Object: Set fso = SetFSO
    BookExists = False
    If fso.fileexists(fullPath) Then BookExists = True
End Function

dim fullPath as string: fullPath = "（ブックのフルパスを記述）"

'フルパスのブックが存在していればブックを開く
dim wb as Workbook
if BookExists(fullPath) then Set wb = OpenBook(fullPath)