What is removed
Only supported entities with the same type, layer and matching geometric segments count as exact duplicates. Reversed LINE endpoints still describe the same segment. Entities on different layers remain separate because layers can represent different operations. The original upload is never modified.
What remains for review
Partial overlaps, intersections, near-duplicates and different segmentation are not merged. Removing them automatically could change the design. Download the report and inspect suspicious locations with a CAD tool that exposes the full topology and intended operation.
Open does not always mean broken
An outline for a closed cut should usually connect, while lettering or engraving may intentionally contain open strokes. Endpoint counts are a diagnostic aid at the tolerance you choose. A tolerance large enough to merge nearby intended features can hide real gaps, so compare it with drawing scale.
Distinguish exact repetition from nearby geometry
Imagine two identical LINE records on CUT with endpoints (0,0) and (100,0). Reversing the endpoints still represents the same segment. Matching geometry with matching remaining attributes can be reduced to one record. A line on ENGRAVE, a line with a different elevation, or one with different non-handle attributes remains because deleting it could change the intended operation.
A second line offset by 0.001 drawing units is not an exact duplicate, even if the endpoint diagnostic groups it at a larger tolerance. Duplicate removal and endpoint grouping answer different questions. Increasing the tolerance is not a way to merge nearly overlapping curves.
Inspect the cleaned file before committing
Run the check, compare the duplicate count with what you expected, then download the cleaned DXF. Open both original and cleaned versions in CAD and compare relevant layers and entity counts. Intentional open engraving strokes may remain open. Closed-cut outlines need separate attention to partial overlaps, crossings and gaps, none of which this exact-duplicate operation automatically repairs or certifies.