// Open the first MHTML file.
Workbook mhtmlFile1 = new Workbook("chartsFileWithPath.mhtml");

// Define the second source book.
// Open the second MHTML file.
Workbook mhtmlFile2 = new Workbook("pictureFileWithPath.mhtml");

// Combining the two workbooks
mhtmlFile1.Combine(mhtmlFile2);

// Save the target book file.
mhtmlFile1.Save("combinedFileWithPath.mhtml");