The yellow paper symbolizes Tom's career ambitions.
The yellow paper is where Tom has for two months been jotting down research statistics on grocery stores in the hopes the report he is about to file will get him ahead at work. When the paper flies out the window and gets stuck on the ledge of Tom's apartment building, he risks his life to retrieve it.
The risky business of climbing out on a high ledge gets even more life threatening when the window he climbed out from slams shut. Tom shoves the yellow paper in his jacket pocket as he makes a life and death effort to fling his arm through the glass and shatter the window. If he fails, he will topple backwards to his death.
Tom succeeds, but after that the yellow paper—Tom's ambitions for future success—seems far less important. If he had died, the yellow paper, the contents of his dead man's pocket, would have meant nothing.
Tom wants to get ahead at work but that quest is pointless if he dies in the process. His brush with death helps Tom to realize that he needs to enjoy the moment, because life is too short and precious to spend all of it on work.