I think, you can implement the following workflow to get the desired output:
1- Use the following code to convert each page of input Word document (generated in STEP1) to a separate PDF file (this is because PageSplitter utility does not produce expected results)
Document doc = new Document(@"D:\Temp\intermediate.doc");
int pageCount = doc.PageCount;
PdfSaveOptions opts = new PdfSaveOptions();
opts.PageCount = 1;
for (int i = 0; i < pageCount; i++)
opts.PageIndex = i;
doc.Save(MyDir + @"18.6-" + i + ".pdf", opts);
2- Use Aspose.PDF for .NET to convert each one Page PDF to separate Word documents:
Convert PDF to DOC or DOCX format
3- Adjusting Top margin with Aspose.Words on first-page Word document will push some content to second page. You then need to repeat 1) and 2) for this document. This will again result in two word documents.
4- Similarly, adjusting the Top margin on last-page Word document will push some content to second page. You then need to repeat 1) and 2) for this document as well. This will again result in two (or more) word documents.
5- For the documents produced in 3) and 4), use Aspose.Words to just remove Top margins from all documents other than the documents corresponding to first and last pages.
6- Append all Word documents in correct order by using Aspose.Words for .NET.