In the following sentence can I use either of the two? step/pace and until/til
It took exactly twenty-five paces(steps) from the office door until(till) her desk.
What sounds more natural to the native ear?
A pace usually means the stride one ordinarily takes in unimpeded walking: roughly thirty inches, or three-quarters of a meter.
But the ancient Roman military passus, usually translated 'pace', was two strides: in marching, the distance between successive strikes of the same heel. The English 'mile' of just over 5,000 feet derives from the Roman mille of one thousand paces.
A step has a broader range: it may be a step up or down, as well as a step on level ground, and even on level ground the particular footing—mud, or snow, or ice, or vegetation—may enforce steps smaller than a full stride.
Accordingly, pace is more usual for approximate measurements.
In your example, however, pace will be appropriate only if the path from the door to the desk is unimpeded—for instance, down an aisle between desks or cubicles. If there are turns or obstacles, step may be all that is enumberable.
Whichever unit of measure you use, the ordinary construction is so many X from A to B, not until or till. Until and till mark endpoints in time, and even there are used mostly for time as experienced rather than measured.
He worked until four o'clock, BUT
He works from nine to five.
It depends. If you want to specify an exact number of steps, then paces sounds more natural:
My sofa is ten paces from the fridge
My sofa is ten steps from the fridge (or My sofa is ten footsteps from the fridge).
In context however, it sounds like twenty-five paces is being as a rough estimate of length, which is why it sounds a little forced. A native would much more likely use an alternative unit of length:
It is twenty-five feet from the office door to her desk.