Thank you for additional information. The problem occurs because you are using floating table in your document. If you specify Text Wrapping of table to None, all will work fine.
Currently there is two methods to convert the document to PDF.
Direct conversion (without using Aspose.Pdf). In case of using direct conversion method, this is issue #6898 in our defect database.
Issue #6898 - Support floating table positioning
Legacy conversion (Aspose.Words+Aspose.Pdf). In case of using legacy conversion this is issue #1001 in our defect database.
Issue #1001 - Add support for ‘text wrapping around’ in word2pdf
I will notify you as soon as these issues are fixed.