You can print to the Windows 10 PDF printer, by using the PrintOut method and specifying the fourth output file name parameter, as in the following example:
/// <summary>
/// Convert a file to PDF using office _Document object
/// </summary>
/// <param name="InputFile">Full path and filename with extension of the file you want to convert from</param>
/// <returns></returns>
public void PrintFile(string InputFile)
{
    // convert input filename to new pdf name
    object OutputFileName = Path.Combine(
        Path.GetDirectoryName(InputFile),
        Path.GetFileNameWithoutExtension(InputFile)+".pdf"
    );
    // Set an object so there is less typing for values not needed
    object missing = System.Reflection.Missing.Value;
    // `doc` is of type `_Document`
    doc.PrintOut(
        ref missing,    // Background
        ref missing,    // Append
        ref missing,    // Range
        OutputFileName, // OutputFileName
        ref missing,    // From
        ref missing,    // To
        ref missing,    // Item
        ref missing,    // Copies
        ref missing,    // Pages
        ref missing,    // PageType
        ref missing,    // PrintToFile
        ref missing,    // Collate
        ref missing,    // ActivePrinterMacGX
        ref missing,    // ManualDuplexPrint
        ref missing,    // PrintZoomColumn
        ref missing,    // PrintZoomRow
        ref missing,    // PrintZoomPaperWidth
        ref missing,    // PrintZoomPaperHeight
    );
}
The OutputFile is a full path string of the input document you would like to convert, and the doc is a regular document object. For more info about the doc please see the following MSDN links for _Document.PrintOut()
The PrintOut in the example results a silent print, when you print through the specified inputFile to the OutputFileName, which will be placed in the same folder as the original document, but it will be in PDF format with the .pdf extension.