PDF Combiner is a user-friendly, GUI-based tool built in
PDF Combiner is a user-friendly open source free to use, GUI-based tool for combining, pdf to excel, pdf to word, image to pdf, zip, unzip annotate and splitting PDF files. It is easy to use, supports multiple file insert and delete and process, and allows you to adjust the order of files before combining.
Convert HTML to PDF in .NET with C# using EVO HTML to PDF for .NET
...EVO HTML to PDF Converter library is also available on various other platforms in various programming languages like Java, Azure, WinRT and Windows Phone, Mono, Xamarin or .NET Core, Linux, MacOS, iOS or Android
JPDF Export is a java library built on the famous iText library. It provides simple functions that can be used to build complex pdf files. It also provides simple classes to merge, split and convert pdf files