If you have say a PDF file or a Word document file on your USB memory stick you cannot view them without software and the Gedcom file is the same, you need software that will recognise and open the file.
Ancestry Trees will not export as an Ancestry Tree, if they did Ancestry would soon loose a huge slice of their subscribers.
The creation of a Gedcom file is best undertaken as a routine process, every week or month depending upon how much new data you have added.