If you open both File,
then select one file,
select all the worksheets in the file
Right click on a Tab and Move, select the other file and Move or Copy
The worksheets and any VBA Code on those worksheets will be moved/Copied
Any VBA Code not on Worksheets but on Code Modules will not be transferred and you will have to do that manually
If you move all the worksheets You will be warned that the workbook is being closed and you may loose code on Code Modules
The easiest way to avoid that is to insert a New Worksheet before you Move the worksheets. Don't move the new worksheet as it is simply keeping the file open