<SUBMISSION>
<ACCESSION-NUMBER>0000020740-16-000109
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20160118
<FILING-DATE>20160119
<DATE-OF-FILING-DATE-CHANGE>20160119
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>CLARCOR INC.
<CIK>0000020740
<ASSIGNED-SIC>3714
<IRS-NUMBER>360922490
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1130
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>840 CRESCENT CENTRE DRIVE
<STREET2>SUITE 600
<CITY>FRANKLIN
<STATE>TN
<ZIP>37067
<PHONE>(615)771-3100
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>840 CRESCENT CENTRE DRIVE
<STREET2>SUITE 600
<CITY>FRANKLIN
<STATE>TN
<ZIP>37067
</MAIL-ADDRESS>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>CLARCOR INC
<DATE-CHANGED>19920703
</FORMER-COMPANY>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>CLARK J L MANUFACTURING CO /DE/
<DATE-CHANGED>19871001
</FORMER-COMPANY>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>Conway Christopher
<CIK>0001495674
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-11024
<FILM-NUMBER>161349347
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>C/O CLARCOR
<STREET2>840 CRESCENT CENTRE DR SUITE 600
<CITY>FRANKLIN
<STATE>TN
<ZIP>37064
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_145324565470059.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-01-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000020740</issuerCik>
        <issuerName>CLARCOR INC.</issuerName>
        <issuerTradingSymbol>CLC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001495674</rptOwnerCik>
            <rptOwnerName>Conway Christopher</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>840 CRESCENT CENTRE DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 600</rptOwnerStreet2>
            <rptOwnerCity>FRANKLIN</rptOwnerCity>
            <rptOwnerState>TN</rptOwnerState>
            <rptOwnerZipCode>37067</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Common Stock Par Value $1.00</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>46.45</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-01-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>120000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>46.45</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2026-01-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock Par Value $1.00</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>120000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>120000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Common Stock Par Value $1.00</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>46.45</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-01-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>12898</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>46.45</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock Par Value $1.00</value>
                </underlyingSecurityTitle>
                <underlyingSecurityValue>
                    <value>12898.0</value>
                </underlyingSecurityValue>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12898</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">25% vesting occurs on 01/18/2017, 2018, 2019 and 2020</footnote>
        <footnote id="F2">RSU's vested 25% on 01/18/2017, 2018, 2019, and 2020</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Michelle J. Pearson, By Power of Attorney</signatureName>
        <signatureDate>2016-01-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
