Size of file is different after I save and want to read it back

LowFatSpread helped me with the solution here:
https://www.experts-exchange.com/questions/28020795/String-or-binary-is-truncated-varbinary-max-field.html?anchorAnswerId=38861456#a38861456

1. I save the file using the method in that solution and I have it below. I put a debug step and the datalength of the doc is 4804

 declare @estring varbinary(max),@i bigint,@l bigint
select @i=1,@l=datalength(@doc)
SELECT 'size before loop'
SELECT DATALENGTH(@l)

OPEN SYMMETRIC KEY MyTableKey DECRYPTION
BY CERTIFICATE EncryptMyCert

declare @temp varbinary(8000)

set @temp=convert(varbinary(8000),'')
set @estring=convert(varbinary(8000),'')

while @i<=@l
BEGIN

       SELECT 
                @estring =  @temp + 
                                 ENCRYPTBYKEY(KEY_GUID('MyTableKey'),
                                              SUBSTRING(@doc, @i,
                                                        CASE WHEN @i + 7899 <= @l
                                                             THEN 7900
                                                             ELSE @l - @i +1            
           
                                                        END))
       
                                                     
                                          
       set @i = @i + 7900 
                                              
                                                        
end 

 SELECT 'size after loop'
SELECT DATALENGTH(@estring) -- size is 4808

Insert into table....
    select ....
             @estring

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This is how I read it back and I have debug steps with the datalength. When I read it back in code, the file is corrupt. Not sure what i need to change

OPEN SYMMETRIC KEY ARMSTableKey DECRYPTION

BY CERTIFICATE EncryptArmsCert


SET NOCOUNT ON;

 declare @estring varbinary(max),@i bigint,@l bigint
select @i=1
SELECT @l= datalength(doc) FROM dbo.DocumentFiles WHERE Id = @Id

declare @temp varbinary(8000)

set @temp=convert(varbinary(8000),'')
set @estring=convert(varbinary(8000),'')

 SELECT 'before loop'
 SELECT '@l'
 SELECT @l  ---***** size is 4804
 
while @i<=@l
BEGIN

      
       SELECT 
                @estring =  @temp + 
                                              SUBSTRING(CONVERT(VARBinary(MAX),DECRYPTBYKEY(Doc)), @i,
                                               --SUBSTRING(Doc, @i,
                                                        CASE WHEN @i + 7899 <= @l
                                                             THEN 7900
                                                             ELSE @l - @i +1            
           
                                                        END)
                   FROM dbo.DocumentFiles WHERE Id = @Id
                                                     
                                          
       set @i = @i + 7900 
                                              
                                                        
end 

SELECT DATALENGTH(@estring) --**** size is 4761

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If I need to do all this in code, i can go that route if this doesnt work