Efficient way to merge multiple PDFs.

Q: I'm looking for the most efficient way to take several PDF files
and combine them into one file.
What I know so far:
1) ImportPages does not accept an arraylist with pages from multiple
2) Using the following code:
For Each PDFFile As String In InputFiles
            'Open document
            InDoc = New PDFDoc(PDFFile)

            'Iterate over pages and add to document
            itrPages = InDoc.GetPageIterator
            While itrPages.HasNext
            End While

Works OK, but the resulting PDF is about 70% larger than the original
for the test I did.

Is there a better way?
A: Use ImportPages() (as in code snippet 6 in PDFPage sample
http://www.pdftron.com/net/samplecode.html#PDFPage) to import
collections of pages coming from the same document. If you need to
merge pages from different document, you would call ImportPages()
multiple times (once for each source document).