PDF isn't designed to be a dynamic file type. It is best considered as an 'electronic printed page'. They were never intended to be edited in the way that, say, a word processor file can be re-edited again and again. Much better to edit the original source document and create a new PDF when required.
However, having said that, OOo provides some limited PDF editing through the use of the
Sun PDF Extension, but that extension is provided to correct typos and make tiny adjustments, not for full scale edits.
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