New Zealand's Chief Censor David Shanks banned the 73-page document on Saturday.
Law Faculty Associate Professor Selene Mize said prosecutions for having the manifesto, described by Mr Shanks as a ''crude booklet'' would likely be brought against people who were ''very open'' about possessing it.
''The most likely prosecutions would be for someone who distributes the manifesto actively, rather than just possessing it.''
The maximum penalties for knowingly being in possession of objectionable materials are a term of imprisonment of up to 10 years or a fine of up to $50,000.
''Certain people are allowed to possess a banned document, but they are very limited e.g. lawyers working on appeals,'' she said.
Generally censorship had to come from the Office of Film and Literature Classification, but there were other specific times when information was restricted, for instance suppression orders to protect the fairness of a trial, and interests such as the privacy of victims.
Most of the time censorship was applied to degrading and violent pornography, but it could happen to other material - for instance documents assisting crime.
Different countries varied in their use of censorship legislation, she said.
For instance in the United States bans were highly unusual, due to the constitutional protection for freedom of expression.
In the past, other publications containing terrorist promotional material have been banned in New Zealand, the censor's office releasing a list of issues of three magazines which have been linked to Isil and Al Qaeda.
The censor's decision to ban the manifesto could potentially be appealed to the Film and Literature Board of Review, Associate Prof Mize said.
The Free Speech Coalition has said the manifesto could be important for society to understand a dark part of New Zealand's history.
''New Zealanders need to be able to understand the nature of evil and how it expresses itself,'' coalition spokesman Stephen Franks said told RNZ on Monday.
However Mr Shanks defended his decision, saying a number of criteria were checked when assessing this sort of material.
''We look for exhortations to kill, exhortations to commit terrorism from someone who has influence and credibility in persuading others to do likewise,'' he said.
Mr Shanks has said people who have downloaded this document, or printed it, should destroy any copies.
