QUES: Immediately Wedderburn volunteered for the British Army but being an exceptionally modest man he enlisted only in the role of private

correct the punctuation.

CORRECTED: Immediately Wedderburn volunteered for the British Army but, being an exceptionally modest man, he enlisted only in the role of private.

QUES: You are welcome to arrive at any time although room access is from after 1500

correct the punctuation.

CORRECTED: You are welcome to arrive at any time, although room access is from after 15.00.

QUES: In the case that your DS file doesnt open it is highly likely that you do not have the correct software application installed on your PC to view or edit DS file extensions

correct the punctuation.

CORRECTED:
In the case that your DS file doesn't open, it is highly likely that you do not have the correct software application installed on your PC to view or edit DS file extensions.