When a file will not open

Read the error message first. It names what failed.

Why will the file not open?

The file is damaged or not a .3mf. Download it again. A partial download is the most common cause. If a slicer is the one refusing it, find its message in fixing errors.

Why are there no print settings?

The file was exported as a model, not saved as a project. Export it again from the slicer as a project. Files from CAD tools never carry settings.

What if the slicer is not recognized?

The file still opens for its geometry. Its settings are readable as text in the Raw tab.

What does Geometry missing mean?

A part of the model is missing from this copy of the file. Open the original. See the file does not contain any geometry data.

Why is the model the wrong size?

An STL has no unit, so a part drawn in inches opens 25.4 times too small. See a model opens at the wrong size.

What does non-manifold mean?

The mesh has holes or extra faces. See repair a .3mf.

Why is a large file slow?

Settings load first, and the mesh follows. A 100 MB file takes a few seconds.

Nothing here matches

Compare your file against the 3MF Core Specification, which defines the package layout and the model tree.