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                   Filed by the Registrant ☑  
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                   Filed by a Party other than the Registrant ☐  
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               Check the appropriate box: 
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               Preliminary Proxy Statement 
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               ☐ 
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               Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) 
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               Definitive Proxy Statement 
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               ☑ 
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               Definitive Additional Materials 
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               Soliciting Material under §240.14a-12 
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               Proto Labs, Inc. 
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               (Name of Registrant as Specified In Its Charter) 
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               (Name of Person(s) Filing Proxy Statement, if other than the Registrant) 
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               Payment of Filing Fee (Check all boxes that apply): 
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               No fee required 
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               Fee paid previously with preliminary materials 
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               Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 
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