Cloudconvert.api NuGet package

To add to what Pete has stated above, you can loop through each URL and create an 'ImportUrlCreateRequest' task for each one, see CloudConvert API[^]

With the below code I am using a list called 'importTasks' to store all the 'ImportUrlCreateRequest tasks' dynamically, then loop through each URL in your list and create an 'ImportUrlCreateRequest' task for each URL. I then use this list to add all 'ImportUrlCreateRequest' tasks dynamically in the Tasks object when creating the job -

//Create your list to store ImportUrlCreateRequest tasks...
List<object> importTasks = new List<object>();

//Your list of URL's...
List<string> pdfUrls = new List<string>
{
    "https://mypdf1/pdf",
    "https://mypdf2/pdf",
//And so on...
};

//Loop through each PDF URL and create ImportUrlCreateRequest tasks... 
foreach (string url in pdfUrls)
{
    importTasks.Add(new ImportUrlCreateRequest
    {
        Url = url
    });
}

//Now create the job with all tasks...
var job = await _cloudConvert.CreateJobAsync(new JobCreateRequest
{
    Tasks = new
    {
        import_tasks = importTasks.ToArray(),
           ImportUrlCreateRequest tasks dynamically
        merge_my_files = new MergeCreateRequest
        {
            Input = "import_tasks",
            Output_Format = CloudConvert.API.Models.Enums.MergeOutputFormat.pdf
        },
        export_it = new ExportUrlCreateRequest
        {
            Input = "merge_my_files"
        }
    }
});