How-to guide
Clouds, comments and stamps on a PDF drawing are separate objects sitting on top of the page - anyone can move, edit or delete them. And a layer that's switched off is still in the file, waiting for someone to switch it back on. Flattening fixes both. Here's how to do it with the free PDF Flatten, which runs in your browser without uploading your drawings.
Open PDF Flatten and choose Choose PDFs, or drop the file onto the page. You can add a whole folder with Choose a folder. Everything happens in your browser tab - nothing is uploaded, and your original file is never changed.
Each file is checked as it comes in. Our ground floor plan was marked needs a look: 1 hidden layer, 4 markups (a revision cloud, a rectangle, a text box and a stamp) and 1 filled-in form field. If a hidden layer has text on it, the text is listed at the top of the panel - here an internal note about the client's budget that was never meant to go out.
Switch the preview to What's hidden. Everything on switched-off layers is shown in red on the page, so you can see exactly where it sits. The layer list shows which layers are off (and will be removed from the file) and which are on (and will be merged into the page).
Switch to After flattening to see the page as it will be sent. It should look the same as it does now - the difference is that the markups become part of the page instead of objects on top of it, and the hidden layer's content is gone. In the free version every markup is drawn in; choosing to remove or keep a type of markup is part of PDF Flatten Pro.
Choose Flatten 1 file (or however many you've added). The flattened copy downloads as name_flattened.pdf. The panel confirms what was left out of the copy, and the summary reads: 1 file flattened, 1 hidden layer removed, 4 markups drawn in.
If you want proof, add the flattened copy back in. Our copy came back as Nothing hidden - no hidden layers and no markups. The cloud, notes, stamp and revision letter are still on the page, but they're now part of the drawing, so nobody can move, edit or delete them.
It makes each page permanent, the way it looks. Content on layers that are switched off is taken out of the file, layers that are on are merged into the page, and markups and filled-in form fields are drawn in so nobody can move, edit or delete them.
Yes. Flattening, the check for hidden layers, the previews and flattening whole folders are free, in your browser and in the Windows app, with no account. PDF Flatten Pro is an optional one-off £9.99 upgrade in the Windows app that adds choosing which layers and markups stay, clean for issue, issue stamps, presets and a flatten log.
No. Everything happens on your computer - inside your browser tab, or in the Windows app. Your originals are never changed; the flattened copies are new files.
Not on its own. Stripping the author, software, file paths, attachments, scripts and CAD private data is the Clean for issue option in PDF Flatten Pro.
Not yet. A PDF encrypted by its author is listed as protected and left alone. Save an unprotected copy from the program that made it first.
