> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pdf.co/llms.txt
> Use this file to discover all available pages before exploring further.

# URL Input and Request Limits

## Supported File Sources

<Info>
  The API supports TLS 1.2 and 1.3 for secure connections. Earlier versions such as TLS 1.0 and 1.1 are deprecated and should be avoided.
</Info>

<Tip>
  **Tip:** For re-usable files (e.g., PDF templates), use `cache:` before the URL\
  (e.g., `cache:https://example.com/file1.pdf`) to reduce repeated downloads and avoid\
  errors like `Access Denied or Too Many Requests`. It stores a local copy of the file after the first download, so it does not need to be fetched again from the original server.
</Tip>

The **PDF.co API** supports publicly accessible links from any source, including [Google Drive](https://drive.google.com), [Dropbox](https://dropbox.com), and [PDF.co Built-In Files Storage](https://app.pdf.co/tools/files).

File inputs are accepted only via URLs and not through direct uploads. If your file is stored locally or not publicly accessible, you must upload it using the
[File Upload](/api-reference/file-upload) endpoints to get a publicly accessible URL.

**For data security**, you have the option to **encrypt output files** and **decrypt input files**.
Learn more about [user-controlled data encryption](/knowledgebase/errors/user-controlled-encryption).

## PDF.co Request size

API requests do not support request sizes of more than `4` megabytes in size. Please ensure that request sizes do not exceed this limit.