PDF (Portable Document Format)
for Digital Preservation and
Delivery
John Laurie
Digital Initiatives Librarian
The University of Auckland Library
National Digital Forum
2012
Issues
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Is PDF good enough?
What’s a maximum file size
PDF/A or simple PDF?
Searchable text or clearscan?
How dirty is our OCR?
Can we attach metadata to PDF files?
Should we be using METS-ALTO instead?
Local PDF collections
at the University of Auckland
• Exam papers (image-only) - DigiTool
• JPS, NZJH, Early NZ Statutes, The Bookshelf B-engine
• Theses, working papers - DSpace
• Course Materials (mainly chapters from books)
– Linked from the Catalogue
Advantages and Disadvantages
• “PDF and PDF/A broadly acceptable for long term digital
archiving”
Seadle, Michael. Library Hi Tech27. 4 (2009): 639-644.
• Widely used, constantly improving, Search engine friendly
• Open standard since 2008
• Read out loud, print
• But simple? Morass of variables in my experience
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Image PDF files are large and slow to load
Editing a problem – crowdsourcing proofreading
Difficult to repurpose as HTML etc
Metadata only at the item level
Scanning for PDF
• Condition of originals
• Target outcomes
searchable text or ClearScan
• 300dpi for clear modern fonts
• 400dpi for older documents and very small fonts
• Adobe Acrobat or FineReader
• Different settings needed for photos and text-only pages
• Black-and-white scans don’t work for historical texts and old
newspapers.
• Splitting born-digital PDFs
Optical Character Recognition (OCR)
• Accuracy depends on document and font getting better all the time
• FineReader better than Adobe Acrobat but doesn’t offer
ClearScan option
• ClearScan vs Searchable image,
dirty OCR hidden behind image
• FineReader offers spell-checking, find and replace editing,
proofreading
• Tables, HTML versions, rekeying
• Pdftotext and other text extractors for indexing
ABBYY FineReader 11
Spellchecking options
PDF text behind image
HTML showing actual text
File Sizes, Optimising files
• Compromise between image quality and overlarge files
• What size is too big?
• Text behind image – I’m saving at 300dpi, 40% quality,
about 200K per page for simple text
• Breaking up into smaller sections
• Batch optimising
• Preservation masters, simple text, saved as 5-6MB TIFF
as part of FineReader files
• Reduce File Size best method but often can’t save as
PDF/A afterwards
PDF/A, PDF/A-1a, PDF/A-1b
• “PDF/A is an ISO-standardized version of the Portable
Document Format (PDF) specialized for the digital
preservation of electronic documents”
• A-1a is stricter than A-1b
• Many PDF files can’t be saved as PDF/A –after “reduce file
size” because it substitutes non-embedded fonts.
• Many fonts not allowed to be embedded?
• Preflight identifies errors.
• Medline wants a PDF/A copy of each article
• PDFs downloaded from EBSCO, Springer and ProQuest not
PDF/A compliant
• Will the smarter computers of the future need embedded
fonts? “As we all get smarter and technology improves the acute concerns about format
obsolescence may diminish” Butch Lazorchak The Signal, Library of Congress
ClearScan vs Searchable image
• Clearscan files are just over half the size, are sharper
and clearer
• No Clearscan option from FineReader (spellcheck, find
and replace editing, TIFF master copies)
• ClearScan substitutes a new font – matches shape not
OCRed text unlike text only PDF, can’t guarantee 100%
accuracy
• But pretty good especially on clean text
Adobe ClearScan example
Text behind image says AkaroQ
Adobe Searchable Image Version
Text behind image says AkaroQ
FineReader Text over the image
FineReader Text over the image (FR
reads Akaroa correctly from the
same TIFF file)
Problems with text extraction for indexing using pdftotext
applet
Search for
the
Problems with text extraction for indexing using pdftotext
applet
Search for
the
And diacritics
PDF XMP metadata
Attaching Dublin Core metadata to PDF documents
PDF files
PDF vs METS-ALTO
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Papers Past and other newspaper projects use METS-ALTO
METS (Metadata Encoding and Transmission Standard) links hierarchy
of pages, sections, articles, issues and volumes, provides for
descriptive and other metadata at each level – structural metadata
ALTO (Analyzed Layout and Text Object) stores layout information
and OCR text, enables page views, article views for newspapers.
CCS (Content Conversion Specialists) have created DocWorks METAe
which automates creation of METS-ALTO files and metadata for
sections
Should we all be using METS-ALTO?
Derivatives (PDF, text, TEI, HTML) complex document structures,
metadata at any level
Websites
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New Zealand Journal of History
http://www.nzjh.auckland.ac.nz/
ResearchSpace Doctoral Theses
https://researchspace.auckland.ac.nz/handle/2292/2
Early New Zealand Statutes
http://www.enzs.auckland.ac.nz/
Early New Zealand Statistics test with PDF and HTML
http://www.thebookshelf.auckland.ac.nz/document.php?wid=1148&action=null