in qlikview, in a store statement, it is one qlikview table into one file.
So you will have to concatenate your table before using the store statement.
your table must have the same name colums, for example :
from table A;
'' as col1
'' as col2
col3 as col1,
col4 as col2
from table B;
Store FileToExport into MyFile.txt (txt);
hope this helps.