How to optimize a program on the .NET Framework (QR-code, document printing)?

Question

.NET

Good day!
The question turned out to be a little generalized, but in short the situation is as follows:
I inherited some application written in C#. And already in 4 copies, for each version of the .NET Framework (2.0, 3.0, 3.5, 4.0, for good, you also need to do 4.5). So, this application prints a document that uses a QR code (via ZXing) and is used for printing MS Report Viewer (in 3 versions, 2005, 2008, 2010).
I would like not to produce such a number of versions of the program, but to combine everything into one. Moreover, there is nothing supernatural, except for a QR code, in it. I myself do not rummage around in the NET framework, so I would be grateful for advice and guidance.
I’ll say a few conditions right away:
1. If possible, refuse to install additional software (as it happened with the Report Viewer)
2. The program must work offline (the option using online services with a QR code will not work)
3. Do not inflate the program to incomprehensible sizes

Answer 1

The version of .Net depends on the platforms on which you plan to use the software. 4.5 is only for 8+, especially to work on the description of the issue, 3.5 is enough (100% coverage of Windows, one version for 3.5 is enough).
Nothing but .Net needs to be installed, although some versions come pre-installed.
QR generators can be found on google, offline as .dll will be.
Printing documents - www.youtube.com/watch?v=XIGJzS4ru4g
Printing in WPF - professorweb.ru/my/WPF/documents_WPF/level28/28_9.php
PrintDocument - class https://msdn.microsoft.com/ru-ru/ library/system.dr... (v=vs.110).aspx