An opaque PDF overlay never removes or deletes the original base page content — it only draws new artwork on top of it. The base PDF's underlying text, vector paths, and images remain fully present in the content stream of the output file, even when the overlay layer is set to opacity 1.0 and visually covers the whole page. Anyone who opens the resulting PDF in a viewer that ignores the overlay, runs an extraction tool, or simply removes the overlay layer can recover the original material. That is why PDF Overlay is positioned as a visual composition tool for letterheads, stamps, borders, and design layers, not as a redaction or content-removal utility. If your goal is to permanently delete text, an image, or metadata from a PDF so it cannot be recovered, you need a tool that rewrites the content stream itself — not one that paints a colored rectangle on top. This article explains exactly what PDF Overlay does to the base content, how the overlay is drawn, what the output preserves, and the practical safety checks to run before you share or print the file.
What "Opaque Overlay" Actually Does in PDF Overlay
Inside PDF Overlay, the term "opaque" refers only to the drawing operation performed on the overlay layer, not to any change made to the base page. The tool embeds each overlay page into the base document, computes a centered, aspect-ratio-preserving fit, and then draws that embedded artwork above the existing base page at the chosen opacity. When you set opacity to 1.0, the overlay layer is drawn at full coverage — but "full coverage" here means the painted pixels, not the underlying content stream.
The base PDF controls the output page count, page order, page boxes, and the artwork that already exists on each page. The overlay layer is rendered afterward, so wherever the overlay is opaque it appears above the existing base artwork. None of the base page instructions are rewritten, flattened, or removed. The vector text, the raster images, the form fields, the annotations, and the metadata in the base document travel into the output unchanged unless the tool specifically drops them as part of its drawing pass.
That distinction is the entire reason the product documentation is explicit about redaction. PDF Overlay is a visual combiner: it is for placing a letterhead on a generated report, adding a prepared border to an exported page, layering a watermark-style design over a template, or pairing a stamp sheet with a working document. It is not a tool for deleting sensitive text or hiding personal data so it cannot be recovered.
Why Hiding a Page Visually Is Not Redaction
Redaction, in the strict document-security sense, means physically removing the characters or pixels from the content stream so they cannot be retrieved by any normal reader. A black rectangle drawn over a name does not redact the name — it only covers it up in one rendering path. Many court filings, HR records, and FOIA releases have leaked data because a reviewer placed an opaque shape on top of text and called the job done, while the underlying characters were still searchable, copyable, and extractable.
The PDF Overlay tool goes even further in the visual-only direction. The overlay pages are embedded as PDF artwork and drawn with the page-drawing method exposed in the underlying library. The original text, vector paths, and images in the base PDF are left in the content stream in the order they were authored. Anyone who strips the overlay layer — by re-rendering the file with a tool that ignores it, by selecting text beneath a fully opaque rectangle, or by running a PDF text extractor — will still see the original content.
This also applies to anything that looks like a signature. Placing a signature-looking image with PDF Overlay does not create a cryptographic digital signature and does not establish signer identity. It only paints a picture that resembles a signature on top of the existing page. For actual signer identity, you need a digital-signature tool that writes a signed-by field into the PDF dictionary.
How to Place an Overlay Without Hiding Content You Need to Keep
If your real goal is to combine pages — for example, to put a letterhead behind an exported invoice — the step-by-step workflow is straightforward, and the same opacity control is what lets you decide how much of the base page shows through.
- Choose a base PDF and an overlay PDF, each non-empty and no larger than 25 MiB. The base PDF must be a valid, unencrypted PDF; PDF Overlay does not bypass password protection on encrypted input files.
- Set overlay opacity from 0.1 to 1. Use a low value (around 0.1 to 0.3) for a faint design element such as a watermark or background logo. Use a higher value (0.7 to 1) only when you genuinely want the overlay to dominate and the base to be decorative.
- Review the documented page mapping rule. If the overlay PDF has exactly one page, that page is repeated on every base page — useful for letterheads, borders, and reusable foreground sheets. If the overlay PDF has more than one page, page 1 maps to base page 1, page 2 maps to base page 2, and so on; base pages beyond the overlay count stay unchanged.
- Select Overlay PDFs to create the combined file. The browser embeds each overlay page, fits it inside the base page while preserving its aspect ratio, centers it horizontally and vertically, and serializes one new PDF for download.
- Download the result, which uses the base filename with -overlay added before the .pdf extension. The original base and overlay files are never overwritten.
- Inspect every important page of the output before you distribute or print it. Zoom in on text, try to select and copy a sentence under a supposedly hidden region, and confirm the result is the visual combination you intended.
What PDF Overlay Preserves and What It Drops
Because the overlay is drawn on top of the base instead of merged into its structure, several properties of the base are preserved automatically and several interactive properties are not. The table below summarizes the behavior, taken from the product's documented limits.
| Aspect of the base PDF | Behavior in PDF Overlay |
|---|---|
| Page count, page order, page boxes | Preserved from the base document |
| Underlying text, vector paths, images | Remain in the content stream; overlay is drawn above them |
| Vector and text in the overlay | Embedded as PDF artwork (not rasterized) where the library supports it |
| Links, comments, form fields, scripts, attachments, outline destinations | Not copied as equivalent interactive objects by this drawing operation |
| Encryption or password protection | Not bypassed; encrypted inputs produce a visible error |
| Blend modes, knockouts, overprint, spot colors, separations | Not inspected; print-critical files need professional preflight |
| Original base and overlay files | Never overwritten; download is a new file |
Two practical consequences follow. First, the overlay layer can render at high quality because it stays vector, but the underlying base content is still recoverable through any normal PDF reader or text-extraction tool. Second, anything interactive on the base page — fillable form fields, internal links, comments — will not behave interactively in the output even though the painted artwork may still be visible.
When an Overlay Is the Right Tool vs. When You Need Real Redaction
PDF Overlay is the right tool when your task is visual composition: placing letterhead above generated pages, adding a prepared border, combining a transparent design layer with a report, or pairing corresponding foreground sheets. The product documentation explicitly groups these use cases together and recommends other tools — Merge PDF for concatenation, Alternate Mix PDF for interleaving, Add Watermark to PDF for generated text marks, and Sign PDF for a drawn-signature workflow — for tasks that look similar but require different operations.
It is the wrong tool when your task is to make content unrecoverable. If you need to permanently remove text such as a Social Security number, account number, name, or medical detail before sending a file outside your organization, you need a redaction workflow that removes the underlying glyphs from the content stream and flattens the result. Hiding those characters with an opaque overlay is not enough; the original characters remain selectable, searchable, and copyable in the output PDF.
The same principle applies to metadata. PDF Overlay preserves the base document's structure, which means properties stored in the PDF information dictionary or XMP metadata stream travel into the output untouched. If you also need to scrub author names, software identifiers, or creation timestamps, plan a separate metadata-cleaning step before or after the overlay pass. For readers who specifically want to confirm that nothing leaves their device during the overlay itself, see the privacy notes in Are Files Uploaded When You Overlay PDF Pages?
Practical Safety Checks Before You Share an Overlaid PDF
Even when your goal is purely visual, a few quick checks will keep an overlay pass from accidentally exposing content you meant to keep private.
- Open the output in a reader and try to select and copy text that sits beneath a fully opaque overlay. If you can highlight it, the content is not removed.
- Run a PDF text extractor on the output and search for the string you intended to hide. If it appears in the extracted text, the overlay is visual only.
- Render the file to images with PDF-to-image tooling and confirm whether the base content is still visible underneath. An overlay that looks solid in one viewer can reveal base artwork in another if the underlying graphics model treats opacity or blending differently.
- Inspect metadata in the PDF information dictionary. Because the base structure is preserved, author, title, subject, and XMP fields carry over from the input.
- Confirm the file you are about to send matches the visual result you intended on every page, not just the first one. Multi-page overlays can leave later base pages unchanged when the overlay runs out of pages, and a stale download cannot replace results from a newer opacity or input choice.
PDF Overlay is honest about what it does: it draws a layer, it does not delete a layer. Treat it accordingly — use it to combine pages visually, and reach for a real redaction tool whenever "remove" must mean "unrecoverable."