I first started with an Excel sheet (.xls extenison) with the title as a header which I then converted into a PDF which looks fine. Then I combined this PDF with various PDF documents (from Word .docx extension) and a PDF document scan. Once all the files were combined, the header of the Excel sheet mysteriously vanished ! (So that it would be visible on the final document I ended up by moving the text of the header to the Excel sheet itself).
Can someone explain this mystery ? Did I do anything wrong ? If yes, an explanation would be greatly appreciated !