TCPDF output without saving file

If You want to open dialogue window in browser to save, not open with PDF browser viewer (I was looking for this solution for a while), You should use 'D':

$pdf->Output('name.pdf', 'D');

This is what I found out in the documentation.

• I : send the file inline to the browser (default). The plug-in is used if available. The name given by name is used when one selects the "Save as" option on the link generating the PDF.
• D : send to the browser and force a file download with the name given by name.
• F : save to a local server file with the name given by name.
• S : return the document as a string (name is ignored).
• FI : equivalent to F + I option
• FD : equivalent to F + D option
• E : return the document as base64 mime multi-part email attachment (RFC 2045)

Hint - with a saving file:

$pdf->Output('sandbox/pdf/example.pdf', 'F');

Use I for "inline" to send the PDF to the browser, opposed to F to save it as a file.

$pdf->Output('name.pdf', 'I');