A lot of free OCR tools online are not actually running their own OCR. They are thin interfaces sitting in front of a metered cloud API, which is exactly why so many of them cap you at a few pages a day or push you toward a paid plan the moment you try to process anything real. PDFHaul's OCR runs on Tesseract, an open-source OCR engine, directly on PDFHaul's own infrastructure. That difference is not just a technical detail. It is the reason the OCR tool can be free with no page limit rather than free with a catch.
What Tesseract Actually Is
Tesseract was originally developed at Hewlett-Packard Labs between 1985 and 1994. It placed among the top performers in a University of Nevada, Las Vegas OCR accuracy competition in 1995, then sat mostly dormant for a decade before HP released it as open source in 2005. Google sponsored its development from 2006 through 2018 and it has continued as an actively maintained open source project since, with version 5 as the current stable release. It is licensed under Apache 2.0, meaning anyone, including a small company like PDFHaul, can use it in a commercial product without paying a licensing fee or a per-page API charge.
This is not a fringe or experimental piece of software. Tesseract has been in continuous use and development for close to two decades since going open source, and it is the engine behind a large share of the OCR tooling used across document management software, digital archives, and research projects worldwide.
Why Open Source Instead of a Cloud OCR API
Commercial cloud OCR services, the kind offered by the major cloud providers, are genuinely good, and they charge per page processed. That per-page cost is the actual reason so many free-sounding OCR tools online are not really free once you go past a handful of pages. The tool has to pass that metered cost on to you somewhere, either as a hard page cap, a subscription, or a credit system.
Running Tesseract directly, on infrastructure PDFHaul controls, sidesteps that cost structure entirely. There is no per-page fee being paid to a third party for every scan processed, which is what makes it possible to keep the OCR tool free and unlimited on web rather than free with a monthly cap.
How PDFHaul Wires It Into the Pipeline
Raw Tesseract takes an image and returns text. Getting from that to a usable, searchable PDF that still looks exactly like the original scan takes additional tooling. PDFHaul uses ocrmypdf as the layer on top of Tesseract, which handles adding the recognized text back into the PDF as an invisible layer positioned exactly behind the original image, so the page still looks identical while becoming fully searchable and copyable.
Before any of that runs, PDFHaul checks the text density of each page to determine whether it actually needs OCR in the first place, so a PDF that already has a text layer is not needlessly reprocessed. Language detection runs automatically across the 15 languages PDFHaul supports, so there is no manual language selection step to get wrong. This entire sequence runs automatically whenever a scanned file goes through PDF to Word, PDF to Excel, PDF to PowerPoint, or Extract Tables, and it is also available as a standalone OCR tool for anyone who just wants a searchable PDF back without converting to another format.
How the Invisible Text Layer Actually Works
For anyone curious about the mechanics rather than just the result, this is the part that makes a scanned PDF searchable without changing how it looks. The PDF format supports a text rendering mode that draws text with zero visible ink, meaning the characters exist in the document and can be selected, copied, and searched, but nothing is actually painted on screen for them. Tesseract identifies each character along with its bounding box coordinates on the page, and ocrmypdf uses those coordinates to place the invisible text precisely behind the corresponding visible pixels in the original scanned image.
The practical effect is that the page still looks exactly like the original photograph or scan when you view it, since the visible layer is untouched, but a click-and-drag text selection or a search now lines up correctly with what is printed on the page. This is also why OCR quality directly affects how well text selection and copy-paste behave afterward. If a character is misread, the invisible text at that position will not match what a person reading the page sees, even though the visible image itself is unaffected.
What This Means for Your Files
Because the OCR itself runs on PDFHaul's own infrastructure rather than being forwarded to a third-party cloud OCR API, your document is not being sent to an additional external service as part of the process. It is processed, converted, and then automatically deleted from PDFHaul's servers two hours later, the same retention policy that applies across every other tool on the site.
Where Tesseract Sits Among OCR Options
Anyone building or evaluating OCR tooling has a few broad categories to choose from. Commercial cloud APIs from the major cloud providers offer strong accuracy and are billed per page or per API call. Newer deep-learning-based open source projects, built on more modern neural network architectures than Tesseract's underlying approach, have emerged in recent years and in some benchmarks edge out Tesseract on specific tasks like scene text or highly stylized fonts. Tesseract remains the most established and widely deployed open source option for standard document OCR specifically, with the longest track record and the broadest existing tooling ecosystem, including ocrmypdf, built around it. PDFHaul's choice to build on Tesseract reflects that maturity and the Apache 2.0 license, which allows it to run without per-page metering, rather than a claim that it universally outperforms every alternative on every input.
Where Tesseract Has Real Limits
Honesty matters more here than a sales pitch. Tesseract is excellent on clean, printed text, and multiple languages are handled well through its trained language models. It is not a machine learning system built specifically around modern deep learning architectures the way some of the newest commercial OCR products are, and on genuinely difficult input, heavily degraded scans, unusual fonts, or dense handwriting, some purpose-built commercial services can edge it out. For the overwhelming majority of everyday scanned documents, contracts, forms, printed letters, invoices, the difference is not something most people will notice. For a narrow set of very hard cases, a dedicated paid service might do marginally better. That trade-off is worth knowing rather than glossing over.
A Real Example
A small business owner has a few years of scanned paper invoices sitting in a folder and wants to search them for every invoice mentioning a specific vendor, without paying for a document management subscription just to search old records. Uploading them one at a time to PDFHaul's OCR tool, each scan gets checked for a text layer, OCR runs automatically where needed through the ocrmypdf and Tesseract pipeline, and the output comes back as a searchable PDF. Ctrl+F for the vendor name across the folder now actually works. No account was required, no per-page fee applied, and each file was gone from PDFHaul's servers two hours after processing.
Frequently Asked Questions
Is Tesseract the same OCR that other free PDF tools use?
Some do use Tesseract or a similar open-source engine, but many free-sounding tools are actually a thin interface in front of a metered commercial cloud OCR API, which is why they cap usage or push you toward a paid tier once you go past light use.
Does using an open-source engine mean the OCR quality is worse?
Not for the vast majority of everyday documents. Tesseract handles clean printed text and multiple languages well. On a narrow set of very difficult inputs, some purpose-built commercial services may perform marginally better, but that gap does not show up for typical scanned contracts, forms, and letters.
Is my file sent to a third-party OCR service?
No. OCR runs on PDFHaul's own infrastructure using Tesseract directly, rather than forwarding the file to an external cloud OCR API. The file is deleted from PDFHaul's servers two hours after processing.
Why don't more free tools just run their own OCR like this?
Running OCR at scale requires infrastructure and engineering investment upfront, whereas calling a metered cloud API is faster to build but comes with an ongoing per-page cost that eventually has to be passed on to users.
Does PDFHaul use a modified or customized version of Tesseract?
PDFHaul runs Tesseract through the ocrmypdf pipeline, which handles positioning the recognized text as an invisible layer behind the original scanned image and manages automatic language detection and text-density checks before OCR runs.
Peter
Founder of PDFHaul and Bultech
Building tools that make working with documents faster and simpler.
