How can I combine multiple PDFs into one PDF without a 3rd party component?
AFAIK C# has no built-in support for handling PDF so what you are asking can not be done without using a 3rd party component or a COTS library.
Regarding libraries there is a myriad of possibilities. Just to point a few:
http://csharp-source.net/open-source/pdf-libraries
http://www.codeproject.com/KB/graphics/giospdfnetlibrary.aspx
The .NET Framework does not contain the ability to modify/create PDFs. You need a 3rd party component to accomplish what you are looking for.
I don't think you can. Opensource component PDFSharp has that functionality, and a nice source code sample on file combining
As others have said, there is nothing built in to do that task. Use iTextSharp with this example code.
Although it has already been said, you can't manipulate PDFs with the built-in libraries of the .NET Framework. I can however recommend http://itextsharp.sourceforge.net/">iTextSharp, which is a .NET port of the Java iText. I have played around with it, and found it to be a very easy tool to use.