i haven't used it yet (although I plan to shortly) but i found itextsharp, which is a .NET library you can use to create PDFs.
I haven't used it on .NET, but have with Java, but nFOP will convert an xml file to a pdf using other files. The nice part is that if you later want to show the same xml file in HTML or in a different format, you just change the xslt.
Here is a short tutorial on using nFOP: http://www.codeproject.com/KB/dotnet/nfop.aspx
I'm working with it now and I've found the following the most useful:
Create PDFs in ASP.NET - getting started with iTextSharp
Tutorials on creating PDF files using C# 2.0
So far I think the library is great but the documentation is not that great.
With the library you have control over the size of the document. You can also insert images. Filling out a form with predefined fields is the easiest, but you can programmatically position text where you want.
For filling out fields you need to check this out:
Fill in PDF Form Fields using the Open Source iTextSharp Dynamic Link Library
Post any specific questions you have.