Autodesk Inventor seems to support STEP product data format (.stp, .step), so it should be possible to use STEP data files and import them to Inventor and use them for making new parts or assemblies (.iam). But perhaps some alternative, 3rd party converters or other 3D modeling tools can be of help here.
Convert ISO-10303 STEP product data to Autodesk Inventor assembly file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert step to iam on Windows
Autodesk Inventor is modeling application used to create 3D digital prototypes.
Convert from step file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.