Convert/Combine Office Document(s) to PDF in background

Adobe Acrobat X Pro 10.1.9

Hello all,

I'm having difficulty with the process converting/combining Microsoft Office filetypes to PDFs using the Right-Click context menu. Often I will convert several XLS & XLSX documents simultaneously.

During this conversion process, the Adobe product opens MS Excel in the foreground for each document. How can I force the Adobe product to open MS Excel  (and other Office filetypes) in the background so that I can continue working in foreground?  This process can sometimes take several minutes, which means I cannot continue working during this time.

Thank you,

Nick