Thank you for contacting Syncfusion support.
Essential DocIO is a native .NET Word library that is used by developers to create, read, write, and convert Microsoft Word documents by using C#, VB.NET, and managed C++ code from any of the .NET platforms.
Regarding ‘Where do I know which DLL version is good for my project?’
Please find the assemblies requirement information for using DocIO library your application based on the platforms, from the below UG documentation link.
Please find the following UG documentation link on how to create Word documents using DocIO?
Please let us know your exact requirements of using DocIO so that we can point out the topics specific to meet your requirement. Also please let us know if are using any other Syncfusion file format libraries for generating files? So that we could suggest you with more appropriate solution at the earliest.