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

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2015-11-23</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001505155</issuerCik>
        <issuerName>Upland Software, Inc.</issuerName>
        <issuerTradingSymbol>UPLD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001165595</rptOwnerCik>
            <rptOwnerName>GLOBAL UNDERVALUED SECURITIES MASTER FUND LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET, SUITE 1900</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Member of 10% owner group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001161175</rptOwnerCik>
            <rptOwnerName>KLEINHEINZ CAPITAL PARTNERS, INC.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET, SUITE 1900</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Member of 10% owner group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001659603</rptOwnerCik>
            <rptOwnerName>MJBW Investments, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET, SUITE 1900</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Member of 10% owner group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001659549</rptOwnerCik>
            <rptOwnerName>MJBW Genpar, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET, SUITE 1900</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Member of 10% owner group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001081865</rptOwnerCik>
            <rptOwnerName>KLEINHEINZ JOHN B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET, SUITE 1900</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Member of 10% owner group</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
                <footnoteId id="F4"/>
                <footnoteId id="F6"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1351159</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
                <footnoteId id="F3"/>
                <footnoteId id="F5"/>
                <footnoteId id="F6"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>192708</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On November 25, 2015, Kleinheinz Capital Partners, Inc. (&quot;Kleinheinz Capital&quot;), MJBW Investments, LP (&quot;MJBW&quot;), MJBW Genpar, LLC (&quot;Genpar&quot;), Global Undervalued Securities Master Fund, L.P. (&quot;Global Master&quot;), and John B. Kleinheinz (&quot;Mr. Kleinheinz&quot;) made a joint filing under Section 13(d) of the Securities Exchange Act of 1934, as amended, relating to the common stock of Upland Software, Inc.  (the &quot;Common Stock&quot;).</footnote>
        <footnote id="F2">Represents shares of Common Stock directly beneficially owned by Global Master.</footnote>
        <footnote id="F3">Represents shares of Common Stock directly beneficially owned by MJBW.</footnote>
        <footnote id="F4">Kleinheinz Capital is the general partner of Global Master and indirectly benefically owns the shares of Common Stock owned by Global Master.</footnote>
        <footnote id="F5">Genpar is the general partner of MJBW and indirectly benefically owns the shares of Common Stock owned by MJBW.</footnote>
        <footnote id="F6">Mr. Kleinheinz is the sole director and President of Kleinheinz Capital and is the sole member and President of Genpar and indirectly beneficially owns the shares of Common Stock owned by Global Master and MJBW.  Mr. Kleinheinz, Kleinheinz Capital and Genpar disclaim any beneficial ownership of shares of Common Stock, except to the extent of any pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ John B. Kleinheinz, President of Kleinheinz Capital Partners, Inc., general partner of Global Undervalued Securities Master Fund, L.P.</signatureName>
        <signatureDate>2015-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ John B. Kleinheinz, President of Kleinheinz Capital Partners, Inc.</signatureName>
        <signatureDate>2015-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ John B. Kleinheinz, President of MJBW Genpar, LLC, general partner of MJBW Investments, LP</signatureName>
        <signatureDate>2015-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ John B. Kleinheinz, President of MJBW Genpar, LLC</signatureName>
        <signatureDate>2015-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ John B. Kleinheinz</signatureName>
        <signatureDate>2015-12-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
