- Is this tool really free and private? My drawings are confidential.
- Yes — completely. The PDF is opened directly in your browser using PDF.js. No data is sent to any server at any point. The annotation canvas and the final redlined PDF are all generated locally on your device. You can use this tool on an air-gapped machine with no internet after the page has loaded (if you cache it), and your drawings remain entirely on your computer.
- What types of MEP drawings can I mark up?
- Any PDF works — HVAC ductwork layouts, plumbing riser diagrams, mechanical equipment plans, electrical single-line diagrams, fire protection plans, structural drawings, site plans, or any other building-systems drawing exported to PDF from AutoCAD, Revit, MicroStation, or similar. As long as it is a valid PDF file, this tool will render and annotate it.
- What redline tools are available?
- There are five markup tools: Pen for freehand redlines and cloud marks; Arrow for pointing to specific items like valves, diffusers, or equipment; Rectangle for boxing out areas that need revision; Circle/Ellipse for calling out pipe connections, sensors, or other round elements; and Text for typed callouts such as "COORD W/ ARCH", "RFI #14", or "REVISE SIZE". You can also choose stroke weight (fine to heavy) and mark color (red, orange, yellow, green, blue).
- How are my annotations embedded in the downloaded PDF?
- When you click "Download Redlined PDF," the tool uses pdf-lib (running in your browser) to embed your annotation layer as a PNG image overlay on top of each page. The underlying drawing data in the original PDF is preserved; the red markup is added as a transparent image layer that sits on top. The result is a standard PDF compatible with Adobe Acrobat, Bluebeam Revu, and any other PDF viewer.
- Can I mark up multi-page drawing sets?
- Yes. Use the Previous / Next page buttons to navigate. Each page has its own independent annotation layer. When you download, annotations from all pages are embedded into the output PDF at once — so you can mark up a full drawing set (mechanical, plumbing, fire protection all in one PDF) and download a single redlined document.
- What is a redline in MEP coordination?
- A redline (or redmark) is a set of hand-drawn or digital annotations made on top of construction drawings to indicate field conditions, design changes, RFI responses, or coordination conflicts. In MEP (Mechanical, Electrical, Plumbing) work, redlines are used by engineers, contractors, and inspectors to mark clashes, route changes, equipment relocations, and as-built deviations. Traditionally done with red pens on paper prints, digital redlines serve the same purpose without printing.