Is it possible to write some text in a PDF (more specifically a link), that will not be printed when sent to a printer, but only be shown in a screen reader?
If it's possible then any pointers to PDF writing .NET libraries that might have this as a feature is very welcome.
There are at least two ways to achieve such an effect with PDF:
put the link or any element you do not want to print on a separate layer (in PDF spec lingo: "optional content") and set this layer as non-printable;
put the link into the PDF as an "annotation" and set this annotation as non-printable.
Related
I have two versions of one same scanned PDF. One of them has an OCR layer. How can I transfer the layer to the other one? I already install Ghostscript, but I don't know what to do next.
How to Use Ghostscript
There's no such thing as an 'OCR layer' in PDF.
Most likely what you have is a PDF file which has a scanned image and the text extracted from that image using OCR which has been drawn as 'invisible' text (text rendering mode 3).
In general you can't copy and paste text between PDF files, so it's very hard to do what you are asking. I don't know of any tools which will help you here, I can say for certain that Ghostscript absolutely will not help you at all.
Most likely you will also need to copy the Font (or CIDFont) from the PDF file as well, and if it has a ToUnicode CMap you'll definitely also want that or search won't work (and there's little point in this sort of OCR otherwise).
Since you have a PDF file which includes the OCR'ed text, why not simply use that PDF ? I can't see any reason why you would want to 'transfer' it to another PDF file.
// 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.
How can I easily crop a PDF page in a given PDF file? I prefer using as little coding as possible, and guess border geometries as little as possible...
There are several options:
Crop by point-and-click using a GUI front-end:
pdf-quench
krop
briss
PDF scissors
Crop by using the command line:
pdfcrop command (provided by texlive-extra-utils), using the following arguments: pdfcrop --margins '-30 -30 -250 -150' --clip input.pdf output.pdf (-left -top -right -bottom format).
PDFCrop
convert -crop command (provided by imagemagick)
Ghostscript
Crop by writing your own script:
Python
LaTeX
For quick, GUI-aided PDF cropping tasks, try pdfarranger (available in Debian repos, formerly known as PDF-Shuffler).
For precise point-and-click cropping, one option is to use LibreOffice Draw.
The instructions below assume you want to crop part of a single-page PDF:
Start with a blank document
Select the Insert > Image... menu
Navigate to the PDF you wish to crop
The contents of the PDF will show up as an image
Right-click on the PDF content in your document and select the "Crop" menu item.
Use the handles to resize the viewable area of the PDF to the section you want to remain after cropping
Click outside of the PDF to disable the crop handles
Click again on the PDF content to position it however you want by:
Dragging it around the page
Using the arrow keys to move it
Use the Draw positioning tools to align or center the PDF content.
When you're happy with the result, save, export it to PDF, or print it.
For multi-page PDFs, You'll have to work page by page by first splitting the PDF into multiple pages using some other tool like PDF Arranger (or simply "Printing to PDF" each page of the PDF you want to crop in your PDF viewer), cropping them one by one with Draw, then recombining them into a single PDF (using PDF Arranger again).
You could try using the pdfCropMargins Python program (https://pypi.org/project/pdfCropMargins/) with the -pg option to select the particular page. The command-line program offers many options, and also has an optional GUI.
You can use Inkscape to losslessly crop PDFs. This uses Inkscape's built-in SVG-PDF conversion.
Open your file in Inkscape: File -> Open -> select your file -> Open
Resize PDF:
Using user-input values: File -> Document properties -> Page -> Custom size
Using auto resize to content: File -> Document properties -> Page -> Custom size -> Resize page to content... -> set desired margin -> Resize page to drawing or selection
Inkscape is a particularly good option as often PDF crop utilities (such as krop, mentioned in other answers) do not change the actual size of the object, instead adjusting how much of the object (e.g. an A4 page) is displayed.
E.g. from krop homepage:
Unfortunately, there is no simple way to eliminate
unnecessary/invisible parts of a PDF file. krop only adjusts which
parts of a PDF are displayed; the original content is still there in
the file and will, for instance, show up when editing the file in
inkscape
Editing directly in Inkscape does exactly what this says is impossible.
The list of tools provided by #sparkler was interesting, but did not help me very much.
Some of the tools provided, actually cropped my pages, but usually they involved some conversion to an image which made pdf files blurry and hard to read.
In the end I used podofocrop of PoDoFo tools which was able to retain all the graphics at full resolution and the text as real text.
It will crop all pages to the minimal size (i.e. without a border).
The command is: podofocrop input.pdf output.pdf
To install on MacOS use brew install podofo
We all know that we can highlight certain texts in a pdf file either using Adobe Acrobat or Preview on Mac. I'm wondering how I can extract all these highlights in a pdf file, and generate a summary (a note kind of thing).
The following post
PDF: standard format for highlights?
points out that there are multiple ways to do highlighting. Will it be a challenge to distinguish the original content of the file and the user-added highlights if shapes with transparency is used to achieve highlights?
Details about this can be found in open source pdf parsing-rendering libraries, and you just have to read the code or document if available.
I've worked on a requirement that allows me to show a PDF file inside a browser by doingo a Response.ContentType = "application/pdf".
The problem is that the default view of the PDF is always showing the bookmarks menu at the left, is there a way by using HTTP headers or something to tell the PDF viewer not to show the bookmarks section?
Thanks in advance.
There's two ways that you can do it. The way that I would recommend is to actually open the PDF in Adobe Acrobat and go to File, Properties. On the Initial View tab you'll see a lot of options for how to display the PDF. The second way I haven't tested but Adobe says you can pass various querystring options to the PDF. The one you'd probably want is http://example.org/doc.pdf#pagemode=none
The way how a PDF document is displayed can be configured inside the PDF document.
There are a lot of PDF editors that can modify the "viewer preferences" as it is mostly called. One free example is BeCyPDFMetaEdit.