Creating a new certificate component as X.509 type and then selecting the certificate import wizard provides an option to select a file containing a private key (.pfx, .p12) or public cert (.cer, .der).
If a public public certificate (.cer or .der) file is selected and saved, then any future re-imports of the certificate must be from a public cert file.
If you try re-importing a .p12 or .pfx file using the same certificate component, the Finish button will be disabled. For security reasons, Boomi will not allow for the re-import of a .p12 or .pfx file to replace a certificate component that was created from a .cer or .der file originally. This is why the Finish button is grayed out.
To import a new certificate component from a .p12 or .pfx files, you will need to create a new certificate component as X.509 type and then select the certificate import wizard to select a .p12 or .pfx file. It may prompt you to enter the certificate password, but then it should let you select the Finish button and save the new certificate component. You will then need to re-select this certificate component in the process or settings where it will be used in the platform.