diff --git a/SKILL.md b/SKILL.md
index 8a29816..679c9b9 100644
--- a/SKILL.md
+++ b/SKILL.md
@@ -153,6 +153,20 @@ After entering bills:
 
 ## Uploading Attachments
 
+### Downloading Invoice PDFs from Email
+
+When emails contain PDF attachments, the Fastmail `include_attachments: true` parameter can cause the result to exceed the token save limit (~25K tokens), truncating the base64 data and making extraction impossible.
+
+**Preferred approach — download from URL first:**
+Many vendor emails (Stripe/Anthropic, Hetzner, etc.) include direct PDF download links in the email body. Extract the URL from `textBody` and download with `curl -sL -o <path> "<url>"`. This is faster and more reliable than attachment extraction.
+
+**Fallback — extract from attachment:**
+Only use `include_attachments: true` if no download URL is available. If the saved result file is truncated (check with `tail -c 200`), the attachment cannot be recovered from that fetch — do not retry parsing.
+
+**File naming convention:** `{Vendor}_{YYYY-MM-DD}_{InvoiceNumber}.pdf` saved to `invoices/`.
+
+### Upload to Grist
+
 ```bash
 # Get session token, then:
 bash scripts/upload-attachment.sh invoice.pdf Bills {id} $TOKEN Invoice