PDF and AI import
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Text editing tips: Any text imported from PDF or AI has each letter's precise place on the page fixed. While this preserves the exact appearance (e.g. justification of text blocks) of the imported document, it makes editing such text difficult: deleting text fails to contract the text line and inserting text fails to expand it, i.e. typed letters overlay the existing letters. (However, you still can replace a letter with another letter of about the same width, although you may need to kern it into place with Alt+arrows.)

To work around this, select the text object you want to edit and use Text > Remove manual kerns command. This will remove the exact positioning information, so if the text block was justified it will lose justification, but instead you will be able to edit it as usual.

Note that there is a way to select even a single line in a text block. For this, open the XML editor, expand the <svg:text> tree branch corresponding to your text, and select any of the <svg:tspan> objects under it. Now you can remove manual kerns from this line only. After you finish editing the line, you can manually justify it back, for example by adding spaces, manual kerns (Alt+arrows), or by adjusting letterspacing (select the whole line and use Alt+> or Alt+<).

The native PDF/AI importer is based on the poppler library and was implemented by Miklós Erdélyi as part of the Google Summer of Code 2007.