PDF markup for construction is software in which builders open the architect's drawings as PDF files, mark changes on them, measure lengths and areas, and send the marked-up set back to the design team. A drawing with these notes on it is called a markup. The software is a part of BIM software work, but contractors use it most, because they usually receive the drawings as PDFs rather than as the model.
Why PDFs? The architect's model sits in the architect's own design software, which the contractor may not have. A PDF can be opened by everyone on the project, on a laptop in the site office or on a tablet on the floor. A general PDF editor can add comments. Construction markup software adds the tools that builders need. It knows the drawing's scale, so it can measure on the drawing. It has standard symbols, such as a revision cloud, a wavy outline drawn round an area that has changed. It can also lay two versions of a drawing over each other and highlight what is different.
Consider a site engineer at a contractor building a school in Mysuru. He receives revision C of the ground-floor plan, drawn at a scale of 1 : 100. He sets the scale in the software by clicking on one dimension that is already written on the drawing. Then he traces the walls of the new science lab. The software reports 46.8 metres of wall and 118 square metres of floor. So the lab floor now needs 118 square metres of tiles, not the 96 square metres in revision B. He also draws a revision cloud round a door that would open into a column, and types a question for the architect.
He sends the marked set back to the architect through a shared session. In the session, the architect's team sees each comment and replies to it. Each markup is saved in a list with its page, its author and its status, so nothing is lost in an email thread. The architect issues revision D. The software lays revision D over revision C, and the engineer confirms that the door has moved away from the column.
Measuring on a drawing in this way is a manual quantity takeoff. For a whole building, the counting is now often done by AI, in quantity takeoff software. Markup software is still used to check those counts, and for every question between the site and the design team.