Quote:
Originally Posted by veole
So what exactly is a PDF Editor and why do companies sell them like "editors"?
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They are sold because people want to buy them. Adobe makes the best one. Nuance makes a pretty good one. As has been mentioned PDF is not a directly editable format like Word or standard word processors. It is a display format that is page oriented. In this way it is similar to the now defunct page maker which has been replaced by PDF. You can modify information within the document but it doesn't do an in place replacement since this would require exact same length changes and adding stuff you disrupt the formatting of other places. Instead it builds a pointer to the new changes that are placed somewhere towards the end of the document. When it is displayed the PDF reader uses the pointer to find the data and then displays it in the correct place. The new data might be a letter or a word and it is as if it were pasted over the original place.
If there is a lot of editing then the display can get really complicated and some readers will have trouble displaying it. In particular converters will have trouble making sense out of it and may make errors in the conversion. There is very little if any semantic information in the document so it is hard to convert. Adobe did spend some time trying to add some semantic data to permit a document to reflow in electronic readers (tagged) and this kind of document is better but even adobe can have trouble reflowing a document that has been edited a lot.
Dale