Learn English – n antonym(…) for “append”

The dictionary says that the meaning of append is to attach something to the end of a document:

append
[uh-pend]
1. to add as a supplement, accessory, or appendix; subjoin: to append a note to a letter.
2. to attach or suspend as a pendant.
3. to sign a document with; affix: to append one's signature to a will.

I'm asking in the prefix, suffix sense here, i.e. append to a word, not a document.

Also here it says that "append" is not restricted to end or beginning, it just means "to attach":

Append simply means "add to" or "attach to"; it's not restricted to adding something to the end of or after something else. An antonym for "append" would therefore be words such as "remove" or " detach, or any word that means "take away from".

So what would be the antonym(or converse, inverse, whichever fits best) for append in this case?
Also what will be the reverse of append, in terms of operation(like prefix is for suffix, which is just joining in the front instead of back)? I thought it would be prepend, but that had a different meaning.