<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2016-05-20</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000827871</issuerCik>
        <issuerName>EAGLE PHARMACEUTICALS, INC.</issuerName>
        <issuerTradingSymbol>EGRX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001674772</rptOwnerCik>
            <rptOwnerName>ProQuest Financial LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2430 VANDERBILT BEACH ROAD, #108-190</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NAPLES</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>34109</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, $0.001 par value</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4770828</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By ProQuest Investments IV, L.P.</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, $0.001 par value</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9360</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The shares are held by ProQuest Investments IV, L.P. (&quot;Investments IV&quot;). which ProQuest Financial  LLC (&quot;ProQuest Financial&quot;) manages pursuant to a management agreement that was assigned from ProQuest Management LLC (&quot;ProQuest Management&quot;) to ProQuest Financial in connection with an internal reorganization. Jay Moorin and Alain Schreiber are managing members of ProQuest Financial and each of them disclaims beneficial ownership of such securities except to the extent of his pecuniary interest in such securities.</footnote>
        <footnote id="F2">The shares were transferred from ProQuest Management to ProQuest Financial in connection with an internal reorganization. Jay Moorin and Alain Schreiber are managing members of ProQuest Financial and each of them disclaims beneficial ownership of such securities except to the extent of his pecuniary interest in such securities.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Pasquale DeAngelis</signatureName>
        <signatureDate>2016-05-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
