Yes, Aspose.Words for .NET supports IF field along with other MS Word supported fields. Fields Overview
You can easily use Mail Merge feature with Aspose.Words for .NET and save output to PDF document. Please note Aspose.Words for .NET does not limit number of pages and output file size. It processes document in memory, so it depends upon system resources. Usually it needs few times more memory than document size to build model of the document in memory. For example, if your document’s size is 1 MB, it needs 10-20 MB of RAM to build its DOM in memory.
I am running through your samples now and trying to integrate one or two of them with our Word Templates. We have one template that is about 28 pages, but because we are using “Trial” software, it quits after about 10-12 pages(not consistent). We don’t want to buy the product unless we know it can handle larger documents both from mail merge to PDF export. Is there anyway I can get past the trial software limit? Thanks.