Compare PDF Drawings with a Revision Overlay
Superimpose two drawings, lined up automatically by position, quarter turn and one uniform scale, so differences become visible for a person to read.
Tool workspace
Nothing is uploaded. Files are read in this tab and stay on your machine.
Overlay two drawings
This tool makes differences visible for a person to read. It does not detect change, and nothing it shows should be treated as an authoritative statement that a drawing did or did not change.
Save your download before you leave the page — it exists only in this tab.
How do I compare two PDF drawings?
For each drawing, set the page number first, then choose the PDF. To change the page later, set the number and choose the file again.
Wait a moment while the two drawings are lined up. The tool says how much of the ink lines up, and tells you plainly when the fit is poor.
Read the comparison: grey is on both drawings, green only on the base drawing, red only on the other. Select Make comparison PDF to save it. If the alignment is wrong, open Adjust the alignment by hand.
How are the two drawings lined up?
Compare two PDF drawings by laying one over the other: choose both files and the second is lined up on the first automatically. Lines on both are grey, and lines on only one are green or red, and you can save the result as a PDF.
The two sheets are first matched by their page size, turned a quarter turn if one is portrait and the other landscape. The tool then finds the small shift and scale a plotter or printer adds by matching the line work of the two drawings, and reports the share of ink that lines up. That is the right model for two revisions of the same drawing, where the sheet may have been re-plotted or printed at a different size but the geometry has not been distorted. Fitting a separate scale per axis would stretch one drawing until it agreed and would hide a real difference, so it is never done. When the automatic fit is poor you can align by hand from two matching points, picked far apart.
How Xenmark makes it easy to compare two PDF drawing revisions
Two revisions, lined up automatically
Choose both drawings and the second is moved, turned and scaled onto the first so the two sheets sit on top of each other, with nothing to click.
Nothing leaves your machine
Nothing is uploaded. Files are read in this tab and processed in memory, with no account and no server for them to go to.
Grey, green and red, saved as a PDF
Lines on both drawings are grey, lines only on the base green and lines only on the other red. Save it as a PDF at the drawing's sheet size, or switch to difference, see-through or side by side.
No stretching to force a match
Only one uniform scale is fitted, never a separate scale for each axis, so the alignment cannot distort a real difference out of sight.
The fit is shown with the result
The share of ink that lines up is shown with the overlay, a poor fit is said plainly instead of shown as a comparison, and the fitted scale and rotation are printed beside it.
Nothing to install
It runs in the browser you already have. There is no plug-in, no desktop application and no sign-up to get through first.
Limitations
What this tool does not do, stated up front.
This makes differences visible for a person to read. It does not detect change, and nothing it shows is an authoritative statement that a drawing did or did not change.
Both pages are rendered previews, 1,400 pixels on the longer side on screen, so fine detail can be lost there; the comparison PDF is drawn at 300 dpi, or a little less on sheets larger than A1. Compare against the drawings themselves before acting on anything it shows.
Automatic alignment finds position, quarter turns and a uniform scale within 8% of the sheet match; small rotations, perspective and per-axis stretching are not corrected. Password-protected PDFs cannot be compared, and each PDF may be up to 150 MiB and 200 pages.
Questions
Does it work if one drawing was printed at a different size?
Yes. The sheets are matched with one uniform scale, a small printer or plotter scaling is found from the drawing itself, and a sheet printed portrait instead of landscape is turned to match, as long as it was not stretched in one direction.
What if the drawings are not lined up correctly?
The tool says when only a small share of the ink lines up and does not show a poor fit as a comparison. Open Adjust the alignment by hand and click the same two features on both drawings, far apart, such as opposite grid intersections. Points on top of each other, or pairs implying an implausible scale, are refused.
Can this tell me what changed?
No. It shows you where the two drawings differ so that you can look. Deciding what a difference means is yours, and the drawings themselves remain the authority. When you need others to review what changed, Xenmark lets reviewers pin numbered comments on the sheet and track each one.
Why did Xenmark build a free drawing comparison tool?
Xenmark AS is a Norwegian software company building browser-based drawing review tools for owners, consultants, operators and other teams that receive and review technical drawings. Those teams handle PDFs every day, and not every file should be sent to a website just to merge, split or check it — a tender document, a client’s drawing set, a revision that is not released yet. So these everyday tools are free and run entirely in your browser: no account, no upload step, and no server ever receives the file. You can check that yourself — open your browser’s network tab, compare two drawings, and watch nothing leave. What this tool cannot do is listed under Limitations above.
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Reviewing the drawings, not just handling the files?
Xenmark is affordable PDF markup and structured drawing review in the browser. Invite reviewers, pin numbered comments on the sheet, track every one by author and status, and export a clean PDF and Excel when the review is done. Unlike these tools, a review is shared, so its drawings are uploaded to your Xenmark project.
Free forever plan. Reviewers you invite never pay.