Learn Polish: Czyżby ten tajny dokument potwierdził spisek? - Could it be that this secret document confirmed the conspiracy?

While czy just asks a neutral yes/no question, czyżby adds a strong layer of surprise, skepticism, or disbelief. It implies the speaker didn't expect this to happen, which is why it translates better to 'Could it be that...?' or 'Is it really true that...?'. It sets an epistemic tone of doubt.

If the subject were 'I' instead of 'this document', how would czyżby and the verb change?

Czyżby can take personal endings in the past tense, just like other particles. If you were a male speaker asking about yourself, you would usually attach the -m ending to the particle rather than the verb, making it Czyżbym potwierdził spisek?. In our sentence, the subject is a third-person noun, so no personal ending is attached to czyżby.

The verb potwierdził is perfective. Could we use the imperfective potwierdzał with czyżby?

Yes, but it changes the meaning. With the perfective potwierdził, you express surprise that the document successfully and definitively confirmed the conspiracy. If you used the imperfective potwierdzał, you would be asking if the document was in the process of confirming it or tended to confirm it.

Why doesn't the word spisek change its ending here, since it is the direct object of the action?