how to combine all .vcf files to single .vcf file manually

Step 1. First Copy all your vcf files into one Folder/directory.
Step 2. Open Windows command prompt (Windows + R),and then type “CMD” to open command prompt and navigate to the destination folder where all your contact files are stored (you can type CD YOUR PATH command to reach to your destination).

Ex: you have copied your vcf files in folder named “singlevcf” then in command prompt type in “E” drive

                                E:

                                cd singlevcf  
Step 3. Enter the following DOS command: copy *.vcf all.vcf

Step 4. Now you will get all your .vcf files merged into single .vcf file, just Import the created single .vcf file whenever required. This single vCard file will also work on your Google account.

SOURCE : how to combine all .vcf files to single .vcf file manually