.....
SourceFile1 = ThisWorkbook.Path & "\" & "Test1.pdf"
SourceFile2 = ThisWorkbook.Path & "\" & "Test4.pdf"
MergedFile1 = ThisWorkbook.Path & "\" & "Output_Acrobat_01.pdf"
MergePDF_02 SourceFile1, SourceFile2, MergedFile1, 2
SourceFile1 = MergedFile1
SourceFile2 = ThisWorkbook.Path & "\" & "Test3.pdf"
MergedFile2 = ThisWorkbook.Path & "\" & "Output_Acrobat_02.pdf"
MergePDF_02 SourceFile1, SourceFile2, MergedFile2, 3
SourceFile1 = MergedFile2
SourceFile2 = ThisWorkbook.Path & "\" & "Test2.pdf"
MergedFile3 = ThisWorkbook.Path & "\" & "Output_Acrobat_03.pdf"
MergePDF_02 SourceFile1, SourceFile2, MergedFile3, 4
.....