I have an attachment on an archived proposal that I would no longer like to be available--can you remove it please?
I can send you the information as needed rather than post it here.
If I understand you correctly... are you saying you want to remove an attachment from a proposal that you sent to a potential client?
If you sent a proposal, then any attachments you sent were part of your proposal sent to a potential client, n an attempt to get hired for a specific job.
The proposal and the attachment belong to the client that you sent them to. You can't edit them.
The fact that you withdrew the proposal means that you are no longer going to be considered for this job.
But the proposal itself, along with the attachment(s), still belong to the client you sent them to.
I don't mean that you awared that prospective client some sort of "license" or "intellectual property rights" associated with the file.
But the file IS in that client's possession. If that client prints the file up as a poster and films a scene in the next Fast and Furious movie with that poster in the background, featured prominently while Vin Diesel and Dwayne Johnson exchange dialogue, there is nothing you could physically do to stop him.
If you want to maintain complete control over something, then by definition you need to not send a copy of it to somebody on the Internet.