I've wondered about this for years and never found an answer. EDIF is a standard, but it's just a netlist.

The problem, as I see it, is that there's no "standard" for schematic symbols. Without that, there's no real way to generate a transferable representation from one proprietary package to another. While most CAE packages are capable of generating and exporting netlists targeted at other vendors' proprietary PCB packages, those are for the purpose of using schematic capture "A" to generate a netlist for PCB editor/router "B" and not for importing schematics from any other package for editing.

Bitmaps provide the easiest display vehicle, but they're awkward to import and edit, except in the crudest way, e.g. using PAINT or similar pixel editors.

DXF format might work, if one had a program that would both import and export it, but generating DXF in the usual way won't preserve symbols. It will draw them, but won't deal with them as an object.

Obviously, it's not an easy problem to solve, else it would have been done by now.

On corollary problem is that of generating portable symbol libraries with sufficient content to enable one to draw a schematic using standard device symbols (e.g. 74xxx logic, passives, op-amps, regulators, etc.)

The old DOS-OrCAD suite had a very handy, though not totally convenient, way of generating symbols and adding them to libraries.

RE