# Preview File

This interface is used to preview a file, it has two prerequisites: one is that the file is not encrypted, and the other is that the file format supports preview.

**HTTP Interface:**

GET   /file/open/

**Request Header:**

| key               | description        | example |
| ----------------- | ------------------ | ------- |
| Account(optional) | file owner account | cX...   |
| Format(optional)  | file format        | png     |

If you fill in the `Account`, the file will be previewed in the file type set by the account. If you fill in the `Format`, it will be previewed in the specified format, account will not work at this time. If you do not fill in either, it will be previewed in the format set by the first owner.

**Request example:**

Open in browser: URL/file/open/


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://doc.cess.network/products/deoss/api_description/preview.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.