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<h2>1. Summary</h2>

Possibly, for August, 2019 there are no programs suitable for all @Doug requirements.

In section “Suggestion” I suggest alternatives. See “Problems” section, to find out what disadvantages of these alternatives do I consider significant.

<hr>

<h2>2. Disclaimer</h2>

This answer is relevant for 19 August, 2019. In the future data of this answer may be obsolete. I hope, that all bugs, that described in my answer, will be fixed.

<hr>

<h2>3. Suggestions</h2>

For example, I selected <a href="https://app.box.com/s/164609vuvxwwp4ynqbofnszgyb1wlucb" rel="nofollow noreferrer"><code>KiraSuperhero.pdf</code></a> — bilingual (Russian and English) PDF file without OCR; it contain first 14 pages of real book (I don't added in example full book, because testing operations for it may take a long time).

<h3>3.1. PDF-XChange Editor (recommended)</h3>

<ul>
<li>Result: <a href="https://app.box.com/s/novrdwg19vh2weadk77blh8g2zk7n74d" rel="nofollow noreferrer"><code>KiraSuperheroPDFXChange.pdf</code></a></li>
</ul>

Unfortunately, you can't <a href="https://forum.tracker-software.com/viewtopic.php?f=63&amp;t=12236" rel="nofollow noreferrer">add OCR layer</a>, use command-line interface. You can use some <a href="http://help.tracker-software.com/PDFXEdit6/default.aspx?pageid=cdm" rel="nofollow noreferrer">PDFXEdit commands</a>, but <a href="https://forum.tracker-software.com/viewtopic.php?f=63&amp;t=12236#p57512" rel="nofollow noreferrer">for OCR actions GUI required</a>.

Download this program (Chocolatey installation <a href="https://chocolatey.org/packages/PDFXchangeEditor" rel="nofollow noreferrer">supported</a>) → <a href="https://www.tracker-software.com/pdf-xchange-ocr" rel="nofollow noreferrer">download pack for your language(s)</a> if needed → <a href="https://www.tracker-software.com/knowledgebase/351-How-do-I-OCR-documents-in-PDF-XChange-Editor-and-PDF-XChange-Viewer" rel="nofollow noreferrer">add OCR to your PDF</a>; settings in my case:

<img src="https://i.imgur.com/qrvoROp.png" alt="X-Change Editor settings">

<h3>3.2. Convert to image and vice versa</h3>

You can convert your PDF to images → Tesseract will add OCR for your images and will convert images to PDF. Use this script for it:



<pre><code>pdftoppm -jpeg KiraSuperhero.pdf KiraSuperhero
mkdir KiraOutput
for %i in (*.jpg) do tesseract %i KiraOutput/%i -l rus+eng pdf
cd KiraOutput
sejda-console merge -f *.pdf -o KiraSuperheroFinal.pdf
</code></pre>

Result — <a href="https://app.box.com/s/52f4bumg1o79mflptf5ronui5gx72l8l" rel="nofollow noreferrer"><code>KiraSuperheroFinal.pdf</code></a>.

Notes:

<ol>
<li>For simplyfying I don't added additional options or commands for better quality and compression, but it would be nice do add it.</li>
<li>I don't know, how question author was going to use the CLI programs and I don't saw his examples; maybe in his cases it would be nice use another commands.</li>
</ol>

For details about this script, please, read section below “Commands description”.

<hr>

<h2>4. Commands description</h2>

<h3>4.1. pdftoppm</h3>

<ol>
<li><a href="https://stackoverflow.com/q/18381713/5951529">Install Poppler for Windows</a> (I add <a href="https://github.com/chocolatey-community/chocolatey-package-requests/issues/654" rel="nofollow noreferrer">request</a>, that Chocolatey installation will possible) — pdftoppm is Poppler part.</li>
<li><a href="https://www.xpdfreader.com/pdftoppm-man.html" rel="nofollow noreferrer">pdftoppm of XpdfReader</a> is another utility with fewer options; please, do not confuse Poppler and XpdfReader versions.</li>
<li><a href="https://www.systutorials.com/docs/linux/man/1-pdftoppm/" rel="nofollow noreferrer">pdftoppm options list</a>. Pay attention to <code>-r</code> and <code>-jpegopt</code>, that set quality of outputed images.</li>
<li>If your PC haven't required fonts, pdftoppm show it. You will need to download fonts from Internet or use fallback fonts.</li>
<li>Converting to TIF doesn't worked for me; convert your PDF to JPG. See my bugreport for details: <a href="https://gitlab.freedesktop.org/poppler/poppler/issues/820" rel="nofollow noreferrer">bug(pdftoppm): -: Error writing TIFF header.</a>.</li>
</ol>

<h3>4.2. Tesseract</h3>

Links:

<ol>
<li><a href="https://github.com/tesseract-ocr/tesseract/wiki#windows" rel="nofollow noreferrer">Windows installation</a>; <a href="https://github.com/chocolatey-community/chocolatey-package-requests/issues/657" rel="nofollow noreferrer">request</a>, that Chocolatey installation will be possible.</li>
<li><a href="https://github.com/tesseract-ocr/tesseract/wiki/Command-Line-Usage" rel="nofollow noreferrer">Command Line Usage</a>.</li>
<li><a href="https://github.com/tesseract-ocr/tesseract/wiki/Command-Line-Usage#searchable-pdf-output" rel="nofollow noreferrer">Searchable PDF output</a>.</li>
<li><a href="https://stackoverflow.com/a/27602888/5951529">How to run Tesseract with multiple languages one time?</a></li>
<li><a href="https://stackoverflow.com/a/31685802/5951529">How to tesseract multiple files in the same folder from command prompt?</a></li>
</ol>

Notes:

<ol>
<li><a href="https://github.com/tesseract-ocr/tesseract/issues/1476#issuecomment-381331331" rel="nofollow noreferrer">Tesseract doesn't support reading PDF files directly</a>; converting to images required.</li>
<li>I <a href="https://www.computerhope.com/issues/ch000742.htm" rel="nofollow noreferrer">create <code>KiraOutput</code> directory</a> and set is as Tesseract output directory, so that the source file <code>KiraSuperhero.pdf</code> will not merged to <code>KiraSuperheroFinal.pdf</code> in next stage.</li>
</ol>

<h3>4.3. Sejda Console merge</h3>

<ol>
<li>Download and unzip sejda-console archive from the <a href="https://github.com/torakiki/sejda/releases" rel="nofollow noreferrer">latest release</a>. <a href="https://github.com/chocolatey-community/chocolatey-package-requests/issues/659" rel="nofollow noreferrer">Request</a>, that Chocolatey installation will be possible.</li>
<li>Run <code>sejda-console merge -h</code> for <code>merge</code> command options list; <code>sejda-console -h</code> — for all sejda-console options.</li>
<li>If you need correctly merge PDF's, filenames of which is numbers without leading zeros (for example, <code>4.pdf</code>, not <code>004.pdf</code>; <code>14.pdf</code>, not <code>014.pdf</code>), please, read <a href="https://softwarerecs.stackexchange.com/a/66401/23324">this my Software Recommendations answer</a>.</li>
</ol>

<hr>

<h2>5. Problems</h2>

<h3>5.1. Both</h3>

PDF-XChange Editor and Tesseract incorrect or doesn't recognize black symbols on grey background. For example, see page 10 of <a href="https://app.box.com/s/novrdwg19vh2weadk77blh8g2zk7n74d" rel="nofollow noreferrer"><code>KiraSuperheroPDFXChange.pdf</code></a> (file from section “PDF-XChange Editor (recommended)” of this answer):

<img src="https://i.imgur.com/DaEUFLY.png" alt="Grey on black">

Symbols inside red rectangle doesn't selectable.

I need edit this PDF page for correct OCR; see “Note” section of this answer for details.

<h3>5.2. PDF-XChange Editor</h3>

I can't use Russian language in version 8 and need downgrade the program. See my bugreport:

<ul>
<li><a href="https://forum.tracker-software.com/viewtopic.php?f=63&amp;t=32964" rel="nofollow noreferrer">question(version8): Russian OCR pack</a></li>
</ul>

<h3>5.3. Tesseract</h3>

5.3.1. Selected area

See <a href="https://app.box.com/s/7tvqsawr1ud5dvsjcnzrhrvpfy8zzt8y" rel="nofollow noreferrer">example PDF</a>, created by tesseract: words selected not completely:

<img src="https://i.imgur.com/hVo0OXd.png" alt="Tesseract selected area">

I reproduce this problem for any language. See my bugreport:

<ul>
<li><a href="https://github.com/UB-Mannheim/tesseract/issues/20" rel="nofollow noreferrer">bug(pdf): incorrect selected area</a></li>
</ul>

5.3.2. non-English languages

Tesseract can have strange output for non-English languages. See my bugreport:

<ul>
<li><a href="https://github.com/UB-Mannheim/tesseract/issues/21" rel="nofollow noreferrer">bug(default): top line doesn't recognize in default mode</a></li>
</ul>

<hr>

<h2>6. Not suitable for requirements</h2>

Requirement 2 of question is <code>Windows native application</code>. I think, tools below don't meet this requirement:

<ul>
<li><a href="https://github.com/tmbdev/ocropy" rel="nofollow noreferrer">ocropy</a></li>
<li><a href="https://pypi.org/project/ocrmypdf/" rel="nofollow noreferrer">OCRMyPDF</a> — <a href="https://github.com/jbarlow83/OCRmyPDF#main-features" rel="nofollow noreferrer">Tesseract-based</a> CLI program (see also <a href="https://github.com/tesseract-ocr/tesseract/wiki/User-Projects-%E2%80%93-3rdParty" rel="nofollow noreferrer">list of third-party Tesseract programs</a>; it haven't tools, that support all requirements of this question author)</li>
</ul>

For this software Windows Subsystem for Linux or Docker required (<a href="https://github.com/tmbdev/ocropy/wiki/FAQ#how-to-install-ocropus-on-windows" rel="nofollow noreferrer">ocropy</a>, <a href="https://ocrmypdf.readthedocs.io/en/latest/installation.html#installing-on-windows" rel="nofollow noreferrer">OCRmyPDF</a> (pip version <a href="https://github.com/jbarlow83/OCRmyPDF/issues/341#issuecomment-453934102" rel="nofollow noreferrer">doesn't supported for Windows users</a>)). IMHO, programs with this hard dependencies can't be considered “Windows native application”.

<hr>

<h2>7. With bugs</h2>

In this section programs with critical bugs for my tasks.

<h3>7.1. k2pdfopt</h3>

<a href="https://willus.com/k2pdfopt/" rel="nofollow noreferrer">k2pdfopt</a> is multifunctional tool with Tesseract-based (<a href="http://www-e.uni-magdeburg.de/jschulen/ocr/" rel="nofollow noreferrer">GOCR</a> also support) OCR feature. This program allows convert PDF to PDF with OCR without intermediate steps. You can try k2pdfopt, but keep in mind, that it add to PDF Cyrillic symbols incorrectly. See my bugreport:

<ul>
<li><a href="https://github.com/Kristinita/SashaMiscellaneous/issues/27" rel="nofollow noreferrer">bug(non-ascii): Cyrillic symbols in generated PDF</a></li>
</ul>

<h3>7.2. Sejda Console pdftojpeg</h3>

<a href="https://github.com/torakiki/sejda" rel="nofollow noreferrer">Sejda</a> is powerful open source SDK for operation to PDF files. pdftojpeg have better conversion from PDF to images, than pdftoppm (see “pdftoppm” section), but have critical bugs:

<ol>
<li>For bilingual documents words can converts incorrectly:

<img src="https://i.imgur.com/oLf05Eq.png" alt="Sejda Bilingual">

<ul>
<li>Bugreport: <a href="https://github.com/torakiki/sejda/issues/366" rel="nofollow noreferrer">bug(pdftojpeg): multilang documents</a></li>
</ul></li>
<li>Images doesn't display in outputed JPEG:

<ul>
<li>Bugreport: <a href="https://github.com/torakiki/sejda/issues/365" rel="nofollow noreferrer">feature_request(pdftojpeg): Cannot read JBIG2 image: jbig2-imageio is not installed</a></li>
</ul></li>
</ol>

<hr>

<h2>8. Not recommended</h2>

<h3>8.1. Obsolete OCR software</h3>

See Wikipedia article <a href="https://en.wikipedia.org/wiki/Comparison_of_optical_character_recognition_software" rel="nofollow noreferrer">Comparison of optical character recognition software</a> for a complete picture of what OCR programs exist:

I don't review in my answer obsolete, not updated for a long time software as Puma.NET and CuneiForm.

<h3>8.2. GOCR</h3>

<ul>
<li><a href="https://willus.com/k2pdfopt/help/ocr.shtml" rel="nofollow noreferrer">k2pdfopt official site</a>:</li>
</ul>

<blockquote>
 GOCR (…) faster than Tesseract by more than a factor of ten, but Tesseract is far more accurate and still reasonably fast (~25 words per second on a modern PC) and also supports multiple languages (GOCR only supports English / ASCII). Because of this, I decided to make Tesseract the default.
</blockquote>

<h3>8.3. ImageMagick</h3>

<a href="https://askubuntu.com/a/50173/582218">Popular</a> answer to question “How to convert PDF to Image?” is ImageMagick. Maybe you will get better results, but I had a bad behavior.

I tried convert to images <a href="https://app.box.com/s/kw9scmio2mtmjocrs9k34pdto31txwln" rel="nofollow noreferrer">full version of my book</a> (317 pages, 18 MB). I ran this command:



<pre><code>magick -density 300 KiraSuperhero.pdf %d.tiff
</code></pre>

My PC with 8 GB RAM hangs → I needed restart it. I reproduced the problem.

I read <a href="https://askubuntu.com/questions/695282#comment1016865_695282">here</a>, <a href="https://serverfault.com/a/146701/351829">here</a> and <a href="https://imagemagick.org/script/command-line-options.php#limit" rel="nofollow noreferrer">here</a> → I set up <a href="https://serverfault.com/a/503379/351829">environment variables</a> → I ran this command:



<pre><code>magick -density 300 -limit memory 256MiB -limit map 512MiB -limit area 256MB KiraSuperhero.pdf %d.tiff
</code></pre>

ImageMagick converted all pages very slow — for 2 hours. pdftoppm makes the same operation for some minutes.

As <a href="https://askubuntu.com/questions/50170/50180#comment475302_50180">zuo user said</a>:

<blockquote>
 <code>pdftoppm</code> is much faster than <code>convert</code>¹
</blockquote>

This is a known problem, see ImageMagick forum threads: “<a href="https://www.imagemagick.org/discourse-server/viewtopic.php?t=31551" rel="nofollow noreferrer">High CPU load when converting images</a>”, <a href="https://www.imagemagick.org/discourse-server/viewtopic.php?t=32767" rel="nofollow noreferrer">“Optimizing <code>convert</code> speed”</a>.

Also, I'm not recommend ImageMagick for converting images to PDF. User Robert Fleming <a href="https://stackoverflow.com/questions/8955425#comment70694684_8955457">said</a>:

<blockquote>
 ImageMagick decodes the JPEG, resulting in <a href="https://en.wikipedia.org/wiki/Generation_loss" rel="nofollow noreferrer">generation loss</a>. Use <a href="https://github.com/josch/img2pdf" rel="nofollow noreferrer">img2pdf</a> instead; it's also 10–100 times faster.
</blockquote>

<hr>

1 — for Windows <a href="https://stackoverflow.com/a/38319795/5951529">use <code>magick</code> command</a> instead of <code>convert</code>

<hr>

<h2>9. Note</h2>

For OCR layer without (or with minimum) errors your PDF must have good quality. If no, improve quality. See links about it from official Tesseract wiki:

<ul>
<li><a href="https://github.com/tesseract-ocr/tesseract/wiki/ImproveQuality#improving-the-quality-of-the-output" rel="nofollow noreferrer">Improving the quality of the output</a></li>
<li><a href="https://github.com/tesseract-ocr/tesseract/wiki/ImproveQuality#tools--libraries" rel="nofollow noreferrer">Tools/libraries for quality improving</a></li>
</ul>

I have seen other similar posts, but none with these specific requests:

<ul>
<li>OCR application that can be run from the command line</li>
<li>Windows native application</li>
<li>Accepts multipage PDF inputs</li>
<li>Can create a PDF file as output with an invisible text layer</li>
<li>Free</li>
</ul>

Can anyone provide suggestions? 

Other software that I've researched that came close but not exactly what I was looking for: Tesseract (does not seem to accept PDF input files), OCRmyPDF (only Linux/UNIX/macOS supported), TrackerSoftware PDF-Tools (not free).

Free OCR command line application for Windows that can add invisible-text layer to PDF?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我也看到过其他类似的帖子，但没有一篇有这样的具体要求：可以从命令行运行的OCR应用程序。Windows本机应用程序接受多页PDF输入可以使用不可见的文本层作为输出创建PDF文件。免费有人能提供建议吗？我研究过的其他软件接近但不是我想要的: Tesseract (似乎不接受PDF输入文件)、OCRmyPDF (只支持Linux/UNIX/macOS )、TrackerSoftware PDF-工具(

问可以在PDF中添加不可见文本层的Windows免费OCR命令行应用程序？
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