There are a couple of ways you can achieve it:
1. Use the Add Check Mark tool under Fill & Sign tab
1) In Foxit Reader/PhantomPDF V10, go to Fill & Sign tab, choose Add Check Mark Tool.
In Foxit PDF Editor V11.0 to V11.1 and Foxit PDF Reader V11.0&above versions, click Protect -- Fill & Sign to active Fill & Sign tab.
In Foxit PDF Editor V11.2.0,please go to Protect>Foxit eSign to activate the "Foxit eSign" tab where you select the Add Check Mark tool there.
In Foxit PDF Editor V11.2.1 and above versions,please go to Foxit eSign tab to select the Add Check Mark Tool.
2)Click on the desired location where you want to add the check mark to create a check mark there.
3)Click on Hand tool or press ESC to exit editing mode.
2. Use the Windings 2 Font
1) In Foxit PDF Reader/Editor, choose Typewrite tool, click on anywhere on the page.
2) Drop down the font list, choose Windings 2
3) Hold down SHIFT keypad on the keyboard, and tap p.
3. Use the Check Box in Foxit PDF Editor
1. In PhantomPDF, go to Form tab, choose Check Box.
2. Click to drag a check box on the page.
3. Click on Hand tool or press ESC to exit editing mode.
4. Click on the check box to add a check mark.
4. Use the keyboard shortcut number
1) In Foxit PDF Reader/Editor, choose Typewriter tool under Comment tab.
2) Hold down ALT key on your keyboard, and press number 41420 on the keypad.
Note: In Windows, the shortcut for the tick mark is ALT+41420.
5. Use the Windows Character Map
1) Press Win+R buttons on your keyboard to open Run... dialog box
2) Type charmap, then click OK button
3) Find, select and copy the check mark, and then paste onto PDF page with Typewriter.