TwoThink PDF blog
Tutorials and techniques
Practical techniques and workflow guides for merging, splitting, compressing, encrypting and converting PDFs — all completed locally in your browser, with nothing uploaded.
Redacting a PDF: local blackouts versus real redaction
How browser-based PDF redaction (a solid black visual block) differs from Adobe's Mark as Redacted, and which one to use for scans and text PDFs.
How to extract text from a PDF: text layer vs scanned OCR (in the browser)
The difference between reading a PDF's text layer and running OCR on a scan, when to force OCR, and how to extract text locally and download it as a TXT file.
Extracting images from a PDF vs converting a PDF to images
What is the difference between pulling out an Image XObject and rendering whole pages, and how to extract embedded images locally and download them as PNGs in bulk.
How to compare two PDFs: contract diffs and the limits of scans
How TwoThink PDF Compare renders two documents side by side, highlights the text differences, skips unchanged pages, and why scanned files need OCR first.
How to add PDF bookmarks: a table of contents for long documents
Add outline bookmarks to a PDF entirely in the browser: no garbled titles, one bookmark per page, batch mode for many files, and nothing is uploaded.
The 18 best free PDF tools of 2026 (no ads, no sign-up)
The full TwoThink PDF toolbox: merge, split, compress, convert to images, add headers and page numbers, extract text and embedded images — all processed locally in your browser.
How to add "Page x of y" headers and footers to a PDF (and skip the cover)
How to add headers, footers and page-number placeholders to a PDF entirely in the browser: no garbled text, a cover page you can skip, and a preview before you download.
How to turn a PDF into one long image for a social post: three steps
PDF previews in chat apps are awkward, and a tall image is much nicer to scroll. Here are the width, quality and sharing notes that matter.
Why sensitive PDFs should not be uploaded anywhere — and what browser-based tools change
CVs, contracts and financial reports can linger on a server for 24 hours or longer after an upload. I now process sensitive PDFs locally in the browser.
No-sign-up PDF tools: which one is the most decent? A 2026 review
I tested iLovePDF, Smallpdf, TinyWow, docsmall and TwoThink, scoring them on whether they are really free, whether they upload your files, and how many ads they show.
Choosing a resolution when converting a PDF to images: 72 / 150 / 300 DPI
For screens, for articles, for the printer — pick the wrong DPI and you get either a blurry image or a painfully large file. I exported the same PDF at three levels and here is the conclusion.
Five ways to watermark a PDF — which one looks most professional?
Centred, tiled, diagonal, a corner logo, or a different watermark per section: five approaches with opacity advice for each.
How to add a password to a PDF: three steps (with a free tool)
Add a lock before sending out a contract, a CV or a transcript. I set an open password with TwoThink in the browser, and the file never leaves my computer.
Editing a PDF you received in WeChat: three ways (no app download)
Your boss sends a PDF over WeChat and wants it changed? First the boundary: TwoThink cannot rewrite the text inside a PDF, but merging, splitting, encrypting and image export all work in a mobile browser.
PDF too big to send? Four compression methods compared
Email caps attachments at 25MB and chat apps are not much better. I tried four ways of compressing the same 48MB PDF and here is which one is worth it.
Combining several images into one PDF: the complete guide (2026)
How do you turn invoices, contracts or holiday photos into a single PDF? I compared three approaches and recommend the browser-based image-to-PDF tool, with nothing to install.