When utilizing your product, I created the following method:
public string Merge(string[] sourceDocuments, string workingDirectory)
{
string convertedFileName = string.Empty;<span style="color:navy;">try</span> { <span style="color:navy;">if</span> (<span style="color:maroon;">sourceDocuments</span>.<span style="color:maroon;">Count</span>() > <span style="color:#dadada;background:#e6ffff;">0</span>) { <span style="color:navy;">string</span> <span style="color:maroon;">localFileName</span> = <span style="color:#a65300;">Path</span>.<span style="color:maroon;">GetFileName</span>(<span style="color:maroon;">sourceDocuments</span>.<span style="color:maroon;">First</span>()); <span style="color:navy;">var</span> <span style="color:maroon;">cachedFileName</span> = <span style="color:#a65300;">Path</span>.<span style="color:maroon;">ChangeExtension</span>(<span style="color:#a65300;">Path</span>.<span style="color:maroon;">Combine</span>(<span style="color:maroon;">workingDirectory</span>, <span style="color:maroon;">localFileName</span>), <span style="background:#ffffe6;">"TMP"</span>); <span style="color:navy;">var</span> <span style="color:maroon;">mergedFileName</span> = <span style="color:#a65300;">Path</span>.<span style="color:maroon;">ChangeExtension</span>(<span style="color:#a65300;">Path</span>.<span style="color:maroon;">Combine</span>(<span style="color:maroon;">workingDirectory</span>, <span style="color:maroon;">localFileName</span>), <span style="background:#ffffe6;">"XLSM"</span>); <span style="color:#a65300;">CellsHelper</span>.<span style="color:maroon;">MergeFiles</span>(<span style="color:maroon;">sourceDocuments</span>, <span style="color:maroon;">cachedFileName</span>, <span style="color:maroon;">mergedFileName</span>); <span style="color:#a65300;">File</span>.<span style="color:maroon;">Delete</span>(<span style="color:maroon;">cachedFileName</span>); <span style="color:maroon;">convertedFileName</span> = <span style="color:navy;">this</span>.<span style="color:maroon;">Convert</span>(<span style="color:maroon;">mergedFileName</span>, <span style="color:maroon;">workingDirectory</span>); } } <span style="color:navy;">catch</span> (<span style="color:#a65300;">Exception</span> <span style="color:maroon;">ex</span>) { <span style="color:navy;">throw</span>; } <span style="color:navy;">return</span> <span style="color:maroon;">convertedFileName</span>;
}