Add pdf redaction configuration docs.

Fixes #181.

docs/docs/filter_policies/pdf.md

@@ -0,0 +1,40 @@
+# PDF Redaction Configuration
+
+PDF redaction can be configured through the `config.pdf` path of a policy.
+
+The available options are:
+
+| Key                      | Type      | Default     | Description                                                                                                                       |
+|--------------------------|-----------|-------------|-----------------------------------------------------------------------------------------------------------------------------------|
+| `redactionColor`         | `string`  | `black`     | This is the color of the redaction boxes that are drawn over the PII. Available options are `white`, `black`, `red`, and `yellow` |
+| `showReplacement`        | `boolean` | `false`     | If `true` then the output of the filter's strategy will be output on the redaction box in the PDF                                 |
+| `replacementFont`        | `string`  | `helvetica` | The font to use for the replacement output. Available options are `helvetica`, `times`, and `courier`                             |
+| `replacementMaxFontSize` | `float`   | `12`        | The maximum font size for the replacement text. Best efforts will be made to fit the replacement text within the redaction box    |
+| `replacementFontColor`   | `string`  | `white`     | The font color for the replacement. Available options match the `redactionColor` options                                          |
+
+### An Example PDF Configuration Policy
+
+The following is an example policy setting the PDF redaction options.
+
+```
+{
+   "name": "example-pdf-policy",
+   "identifiers": {
+      "emailAddress": {
+         "emailAddressFilterStrategies": [
+            {
+               "strategy": "REDACT",
+               "redactionFormat": "{{{REDACTED-%t}}}"
+            }
+         ]
+      }
+   },
+   "config": {
+     "pdf": {
+        "redactionColor": "red",
+        "showReplacement": true,
+        "replacementFontColor": "yellow"
+     }
+   }
+}
+```