Difference between revisions of "Writer/ToDo/PDF Import"

Revision as of 12:29, 29 November 2007

Motivation

PDF is a widely used format to exchange documents containing text and graphics between different applications and different platforms. OpenOffice.org is currently able to create such PDF documents via export filters that are already available within every major OpenOffice.org application. Unfortunately, OpenOffice.org is not able to import PDF documents back again, although this is one of the more often requested features.

See issue 10384 for further details.

Goals for a PDF import

The document created by importing a PDF file should resemble the original as close as possible; nevertheless PDF per se does not lend itself to that end easily: most PDF files contain no information about layout or document structure at all. Therefore a PDF file will never be able to be imported on a 1:1 basis. We have to define goals to define what level of similarity must be achieved on a basis of feasibility.

These goals should be treated as paramount:

• all text that is visible in the original PDF document should be imported
• text attributes: font family, font size, weight (bold, not bold), style (italic, not italic) should be imported together with the respective text.
• all drawing elements (images, vector graphics) should be imported.
• if the implementation has to choose between layout fidelity and editability, lean towards layout.

Additionally there are some goals that would greatly enhance the import result, all of these features can by their nature only be implemented with heuristic methods since PDF (unless the file uses tagged PDF) does not contain structural information. The following text features should be detected (sequence in descending importance):

• Paragraphs
• Enumerations
• Titles
• Underlined text
• subscript/superscript

Use-Cases

There are 3 use cases for a PDF-input filter. To better understand what should be developed, I will separately address these use cases:

• Text-Stream Import
• Text + Layout Import (non-editable)
• Text + Layout Import (fully editable)

Discoleo 18:37, 7 October 2007 (CEST)

Text-Stream Import

Sometimes, people want to import mainly the text-stream to edit it in their preferred program and use it in their own work. In these instances, the exact layout is not that important, and what the import filter should do is:

• generate a continuous text stream [i.e. NOT just every line terminated by CR/LF, like the current Adobe Acrobat select tool]
• optimally detect some text-structure:
  • like sub-/super-script
  • paragraphs
  • tables
  • underlined text

Text + Layout (as background)

Users need sometimes to complete a document/form. Often, governments and other institutions publish official documents in pdf-format (simple PDFs, NOT pdf-forms), BUT one cannot add/write any text to these simple pdf documents.

The import-filter should therefore:

• import the pdf (both text-streams and layout) as a background
• users shall be able to write new text in the foreground, overlaid over the background document
  • however, this should be handled better than pasting the pdf-document as an image and writing over the image
  • images create bigger size; poor zooming; difficulty accurately positioning new text to fit the existing text line, ...
  • it should be possible to position the cursor on the baseline of an existing text-line, so that newly written text fits the existing text
  • the tool should detect existing text-box boundaries, so that one can write new text extending from those boundaries
• optimally, some minimal 'pdf-editing' features should be possible
  • move whole sections (text+graphic+layout from the remaining document) downwards, e.g. if the new text does NOT fit in the existing free space

Text + Layout (fully editable)

Of course, this would be a nice feature, BUT - considering the pdf format -, this seems a little bit elusive.

However, pdf-documents saved by OOo should contain additional information, that should allow importing them in OOo in a fully editable state. At least OOo-generated documents shall allow this editing mode.

Another approach could be to allow importing PDF to Impress or Draw to edit the complete layout, by treating it as a poster instead of a document (which may be repaginated etc).

Implementation

We will try to come up with a first prototype soon, most probably using an out-of-process xpdf instance to do the parsing (due to license issues). Here's a list of things to do: