Compress troubleshooting: PDF won't shrink, password errors, and lost text

Compress runs entirely in your browser — your PDF is never uploaded — so most problems come down to the file itself or the mode you picked. Here are the common ones and how to fix them.

"This PDF is password-protected, so it can't be opened to compress"

Cause: The PDF requires a password just to open it, so the compressor can't read its pages. (PDFs that only restrict editing or printing — an owner password without an open password — don't trigger this and compress normally.)

1. Open Unlock — the error message links there as "Remove the password first →".
2. Enter the PDF's password to produce an unlocked copy. This also happens locally; the password and file stay on your device.
3. Bring the unlocked copy back to Compress and run it again.

"This PDF is already well-optimized — we couldn't make it smaller without lowering quality"

Cause: This isn't an error — it's the size guard doing its job. Both modes compare the output against your original, and if the result wouldn't actually be smaller, AttachKit keeps the original instead of giving you a bigger file labelled "compressed". It's common with small text-only PDFs in Keep text (lossless) mode, where there's little structural bloat to remove.

1. If you ran Keep text (lossless), the result card offers a direct link to switch to Make it smaller (flatten) — click it, then click Compress PDF again. Flattening re-renders pages as downsampled images and usually wins on scans and image-heavy files.
2. If even flatten mode can't shrink it, the file is already efficiently encoded at that quality level, and making it smaller would mean visibly degrading it — AttachKit won't do that silently.
3. If you're trying to get under an upload limit, consider splitting the document instead with Pages and sending it in parts.

Text isn't selectable or searchable after compressing

Cause: You used Make it smaller (flatten) mode, which re-renders each page as a JPEG image (about 120 DPI). That's where its big savings come from, but it means the pages no longer contain real text — only pictures of text. The tool shows an amber notice about this whenever flattening was actually applied.

1. If you still have the original PDF, re-compress it with Keep text (lossless) instead. Savings are smaller, but text stays selectable.
2. If you only have the flattened copy, run it through Searchable (OCR) — the notice in the result screen links there. OCR adds a text layer back so the document is selectable and searchable again.
3. Note that OCR-recovered text is a recognition of the page image, not the original text, so spot-check anything critical.

Compressing a large file is slow, or the tab feels stuck

Cause: All the work happens on your device — pages are rendered one at a time in your browser rather than on a server. A long scanned document in flatten mode is the heaviest case. To keep memory bounded, very large pages are rendered with their longest edge capped at 2200 px.

1. Wait for the Compressing… button to finish — long scans can take a while, and progress is normal even if the page looks quiet.
2. Close other heavy tabs to free memory, especially on phones and low-RAM machines.
3. For very long documents, split them first with Pages and compress the parts separately.

"Couldn't compress this PDF — it may be corrupted or in an unsupported format"

Cause: The file couldn't be parsed as a usable PDF. It may be damaged, truncated by a bad download or email transfer, or not really a PDF (e.g. a renamed image or Word file).

1. Confirm the file opens in another PDF viewer. If it doesn't open anywhere, re-download or re-export it from the source.
2. If it's not actually a PDF, convert it first — for images, use JPG to PDF.
3. If the file opens fine elsewhere but still fails here, report it — that's a case the team wants to see.

Still stuck?

If none of these match what you're seeing, contact support and describe what happened — since your file never leaves your browser, support can't see it, so include the file's size, page count, and which mode you used.