Microsoft Visio | How to perform VSTO (or alternative) from a Server

Objective:

1. I have a Web Application.
2. I have some Microsoft Visio files present in my Application.
3. I want to process (edit/export/print) these Visio files (Note: Opensource tools like LibreOffice Draw are not giving the same quality like Visio)

Current Progress: I got to know about Microsoft VSTO and achieved some basic operation by using VSTO

Sample code of VSTO

string docPath = "input.vsdx";

this.Application.Documents.Open(docPath);

int pageIndex = 1;
Visio.Pages visioDocPages = this.Application.ActiveDocument.Pages;
if (pageIndex <= visioDocPages.Count) {
// Use `visioDocPages[pageIndex]` for some processing
}


this.Application.ActiveDocument.Close();

Queries:

1. VSTO seems to be an Automation library, so I fear it will fail when multiple files needs to be processed from a Server
2. Are there any other methods to work on visio (like edit, export, print, etc) from a Server environment
3. Am looking for either officail Microsoft packages OR Open Source ones (NOT looking for paid packages like https://products.aspose.com/diagram/net/)