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

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-06-15</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001086909</issuerCik>
        <issuerName>BROADSOFT INC</issuerName>
        <issuerTradingSymbol>BSFT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001125511</rptOwnerCik>
            <rptOwnerName>GROTECH PARTNERS VI LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GROTECH VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>8000 TOWERS CRESCENT DRIVE, SUITE 850</rptOwnerStreet2>
            <rptOwnerCity>VIENNA,</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22182</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001235056</rptOwnerCik>
            <rptOwnerName>GROTECH CAPITAL GROUP VI LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GROTECH VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>8000 TOWERS CRESCENT DRIVE, SUITE 850</rptOwnerStreet2>
            <rptOwnerCity>VIENNA,</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22182</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001235111</rptOwnerCik>
            <rptOwnerName>ADAMS FRANK A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GROTECH VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>8000 TOWERS CRESCENT DRIVE, SUITE 850</rptOwnerStreet2>
            <rptOwnerCity>VIENNA,</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22182</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Series C-1 Convertible Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2402693</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The Series C-1 Convertible Preferred Stock is convertible at any time, at the holder's election, on a one-for-one basis and has no expiration date.  The Series C-1 Convertible Preferred Stock will convert into common stock upon the closing of the Issuer's initial public offering.</footnote>
        <footnote id="F2">Consists of securities held directly by Grotech Partners VI, L.P. (&quot;Grotech VI&quot;).  Grotech Capital Group VI, LLC (&quot;GCG VI&quot;) is the sole general partner of Grotech VI.  Frank A. Adams (&quot;Adams&quot;) is a General Partner of GCG VI.  In addition, Joseph R. Zell (&quot;Zell&quot;) is also a General Partner of GCG VI and a director of the Issuer.  Zell shares voting and dispositive power over the shares held by Grotech VI with Adams.  Zell has filed a separate Form 3 with the SEC on June 15, 2010.  Each of the reporting persons disclaims beneficial ownership of the securities held by Grotech VI, except to the extent of his or its pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Frank A. Adams, as a General Partner of Grotech Capital Group VI, LLC, the general partner of Grotech Partners VI, L.P.</signatureName>
        <signatureDate>2010-06-15</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Frank A. Adams, as a General Partner of Grotech Capital Group VI, LLC</signatureName>
        <signatureDate>2010-06-15</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Frank A. Adams</signatureName>
        <signatureDate>2010-06-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
