I have this PDF ebook with selectable text - the handwriting - but there is no such font embedded and the letters are all different, so it's not actually a font. How is this possible?
I've worked with CorelDraw and Adobe Acrobat, but I can't understand how this works.
The left side of the picture shows the document properties, the right side shows a page of the PDF file and I selected the last 3 rows. I can copy and paste that to a text file, no problem. How was this achieved?
There are a few possibilities but the most likely is the text is being converted to outlines/paths or vectors. Some software such as Adobe InDesign and other print design apps allow you to 'flatten' a font based text into vector or paths, meaning the original font isn't required to be embedded or installed on the system. The original text data is however still present and able to be copied into a text field or word processor.
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// EDIT 26.03.2018 - Who wants to continue my work can have a look on my source-files https://github.com/n0l0cale/ocr-sampledata
I'm actually looking for some details about PDF Files. It's most important for me that the files will be usable for a very long time and if possible the OCR should be automatically applied for new files (which seems to be not really possible with Adobe Acrobat...).
For that I've been looking for different solutions how to OCR my PDF Files. I found three candidates which seems to be doing what they should do... (more or less). But all three variants have their pro&cons... But there seem to be different approaches how to store data in PDF Files.... for all three Variants... Let me explain:
a File OCRed with Adobe Acrobat:
https://github.com/n0l0cale/ocr-sampledata/blob/master/A4%20sample_ACROBAT.pdf
results in a file that Acrobat is able to open in one step (no preloading of any background layer) and after a preflight-script I'm able to see the text which is stored hidden:
a File OCRed with Abby Finereader:
https://github.com/n0l0cale/ocr-sampledata/blob/master/A4%20sample_ABBY.pdf
does not seem suitable for the default adobe preflight-script as it does not display any additional layers:
But far as I was able to reproduce these Files seems to have a Background-Text-Layer, which contains the OCRed Text, which is the underlying layer for the Image that is shown to the user at the end. Unfortunately this seems to be loaded separately and this is confusing while opening the file with Adobe Acrobat...
a File OCRed with Tesseract 4 (Alpha):
https://github.com/n0l0cale/ocr-sampledata/blob/master/A4%20sample_TESSERACT_oem2.pdf
is also doing some weird magic with the hidden text part:
But in all three cases I'm able to search for words in the files and see the text using "Remove hidden information" and selecting "hidden text":
I'm seriously confused.... Does anyone know how these programs are storing their hidden text information really?
S.
P.S.: For those wondering what this ominous preflight script is: https://theblog.adobe.com/hidden-gems-in-acrobat-dc-how-to-optimize-hidden-ocr-text/
Does anyone know how these programs are storing their hidden text information really?
You correctly have found out that the approach of Abby Finereader is different from that of Adobe Acrobat and of Tesseract:
Abby creates a page content stream in which first the text is drawn normally on the page and eventually covered by the scanned image.
Acrobat and Tesseract create content streams in which first the image is drawn and then the text is drawn invisibly (using text rendering mode 3 which draws nothing).
The difference between the latter two results is the choice of font used:
Acrobat uses regular standard 14 fonts for which a PDF viewer has a font program to render them as normal glyphs.
Tesseract uses a font GlyphLessFont it embeds a font program for into the result file. When rendered the glyphs in this font do not show as our normal Latin glyphs but merely as empty space.
Considering the visual effect you observed for the Abby result, the approach used by Acrobat or Tesseract might be preferable.
Whether one prefers fonts with visually recognizable glyphs (as used by Acrobat) or without (as used by Tesseract), is mostly a mere matter of taste. They are used only in the invisible rendering mode anyways.
I made a PDF file from Latex (using TexMaker).
Acrobat Reader is able to display BOTH the text and the table of contents in Linux.
But Acrobat Reader is unable to display the table of contents in Windows XP (the Chinese characters came out as boxes). However, the text is displayed correctly.
I tried to embed the fonts into the PDF but the various methods are not 100% successful, so I'm not sure if the fonts are embedded correctly or not. Anyway, the table of contents remain unreadable in Windows.
I wonder if it is really an font embedding problem? Or do I need to install these "Adobe Reader X Font Packs":
https://www.adobe.com/support/downloads/detail.jsp?ftpID=4883
My concern is that I'd like my PDF to be readable in Windows, including the table of contents (and preferably without further installations). If this is possible...
I suspect you are talking about "bookmarks" and not saying part of the text in the document is ok and part is not. PDF Bookmarks are part of the UI of the application and are not selected from embedded fonts. Therefore, the system you are running on needs to know how to handle fonts in the language(s) of choice.
See https://forums.adobe.com/thread/1144972?start=0&tstart=0
Embedding the fonts will have no effect on the bookmarks.
I have a visual basic program that extracts text from a PDF and imports the text into excel. It relies on reading the text like a human, reading left to right across the page. However, there are instances on this particular PDF where if I go to select the text with my mouse, I click and drag straight across but Adobe starts to select/highlight words on the above and below lines before continuing to highlight across the page. This gives me data that I do not want/need. The page has renderable text and is not from a scanned document.
Is there a way to "reset" the way Adobe interprets the text on the PDF? Since the information on the left is far from the information on the right, it treats them almost like separate columns.
I've tried saving the PDF in different formats such as a txt or postscript and distilling to another PDF but they all seem to result in the same outcome. This is weird to me because I have other similar PDFs where this isn't an issue.
Any help or thoughts would be greatly appreciated, thanks.
As PDF (in its basic form) essentially means placing strings on a canvas, the concept of "sentence" or "reading order" is not built in.
In order to extract text, you would have to read out the bounding box of the piece of text, and then use some logic and heuristics to assemble your text based on the coordinates of the bounding box.
Things can be easier if the PDF is a structured PDF, where the text contents is embedded as text in the document. This is also the prime requirement for an accessible document. So, if your document is accessible, you can rely on the structure for the correct reading order.
I have a piece of software called PDF2XL which is normally great for extracting tables of data from PDF files. I've used it with hundreds of files before.
This one file though, gives me gibberish output that I can't even copy and paste into this textarea correctly. All sorts of unicode weirdness.
If I copy and paste as per normal into excel/notepad I get the same issue.
I assume it's something to do with a messed up character encoding header in the PDF file? How can I change this? I'm on Windows and have no software that can edit PDFs, so if I need to edit/re-save it, please recommend a free piece of SW to do it.
Thanks!
There are an increasing number of PDF files the used subsetted fonts which is basically a custom encoding. Normally the font descriptor in the PDF should have a ToUnicode table to allow the text extraction to decode the font encoding and return the correct text.
Some PDF producers are doing this on purpose to prevent easy PDF text extraction for things such as financial reports. If there is only one font then you could manually decode the font but in my experience I have seen PDF's with multiple random encodings which makes it nearly impossible to decode automatically.
One way to test for these types of PDF's is to open the file in Acrobat, select some text, copy it and then paste it into Notepad. If the text is garbled then the PDF is using a subsetted font and there is not much more you can do. If Acrobat can't extract the text correctly then nothing else can. It may as well be a page of hieroglyphs.
I have PDF files with text that should be replaced. More specificly, the text should be translated and replaced with the translated version.
It's important that the rest of the PDF structure stays intact. Note that the text is available in the PDFs and techniques like OCr are not needed. Also, it would be nice if font and other text attributes are kept.
Which libraries would you recommend for extracting the text to an easy to edit format (such as CSV) and put the new text back in again?
Assuming you are replacing text with a different language, you will have to choose a different font in most cases, and the font choice is non-trivial. I've used the Foxit libraries to change text or create PDFs with success.