kamkar, where are you located?
There are some differences in the rules of each country (and sometimes state) regarding use and disclosure of pseudonyms,aliases, etc.
You need to investigate the rules of the country where the agreement(s) you sign is/are enforced as well as those of the country where you reside.
Keep in mind that it is extremely likely that a document signed by you as [pseudonym] that does not disclose your legal name is probably not valid, almost certainly not enforceable and may open you to charges of fraud, as well.
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